NSABP FB-10: a phase Ib/II trial evaluating ado-trastuzumab emtansine (T-DM1) with neratinib in women with metastatic HER2-positive breast cancer

BACKGROUND

We previously reported our phase Ib trial, testing the safety, tolerability, and efficacy of T-DM1 + neratinib in HER2-positive metastatic breast cancer patients. Patients with ERBB2 amplification in ctDNA had deeper and more durable responses. This study extends these observations with in-depth analysis of molecular markers and mechanisms of resistance in additional patients.

METHODS

Forty-nine HER2-positive patients (determined locally) who progressed on-treatment with trastuzumab + pertuzumab were enrolled in this phase Ib/II study. Mutations and HER2 amplifications were assessed in ctDNA before (C1D1) and on-treatment (C2D1) with the Guardant360 assay. Archived tissue (TP0) and study entry biopsies (TP1) were assayed for whole transcriptome, HER2 copy number, and mutations, with Ampli-Seq, and centrally for HER2 with CLIA assays. Patient responses were assessed with RECIST v1.1, and Molecular Response with the Guardant360 Response algorithm.

RESULTS

The ORR in phase II was 7/22 (32%), which included all patients who had at least one dose of study therapy. In phase I, the ORR was 12/19 (63%), which included only patients who were considered evaluable, having received their first scan at 6 weeks. Central confirmation of HER2-positivity was found in 83% (30/36) of the TP0 samples. HER2-amplified ctDNA was found at C1D1 in 48% (20/42) of samples. Patients with ctHER2-amp versus non-amplified HER2 ctDNA determined in C1D1 ctDNA had a longer median progression-free survival (PFS): 480 days versus 60 days (P = 0.015). Molecular Response scores were significantly associated with both PFS (HR 0.28, 0.09-0.90, P = 0.033) and best response (P = 0.037). All five of the patients with ctHER2-amp at C1D1 who had undetectable ctDNA after study therapy had an objective response. Patients whose ctHER2-amp decreased on-treatment had better outcomes than patients whose ctHER2-amp remained unchanged. HER2 RNA levels show a correlation to HER2 CLIA IHC status and were significantly higher in patients with clinically documented responses compared to patients with progressive disease (P = 0.03).

CONCLUSIONS

The following biomarkers were associated with better outcomes for patients treated with T-DM1 + neratinib: (1) ctHER2-amp (C1D1) or in TP1; (2) Molecular Response scores; (3) loss of detectable ctDNA; (4) RNA levels of HER2; and (5) on-treatment loss of detectable ctHER2-amp. HER2 transcriptional and IHC/FISH status identify HER2-low cases (IHC 1+ or IHC 2+ and FISH negative) in these heavily anti-HER2 treated patients. Due to the small number of patients and samples in this study, the associations we have shown are for hypothesis generation only and remain to be validated in future studies. Clinical Trials registration NCT02236000.

Prospective Correlation of Magnetic Resonance Tumor Regression Grade With Pathologic Outcomes in Total Neoadjuvant Therapy for Rectal Adenocarcinoma

PURPOSE

Total neoadjuvant therapy (TNT) is a newly established standard treatment for rectal adenocarcinoma. Current methods to communicate magnitudes of regression during TNT are subjective and imprecise. Magnetic resonance tumor regression grade (MR-TRG) is an existing, but rarely used, regression grading system. Prospective validation of MR-TRG correlation with pathologic response in patients undergoing TNT is lacking. Utility of adding diffusion-weighted imaging to MR-TRG is also unknown.

METHODS

We conducted a multi-institutional prospective imaging substudy within NRG-GI002 (ClinicalTrials.gov identifier: NCT02921256) examining the ability of MR-based imaging to predict pathologic complete response (pCR) and correlate MR-TRG with the pathologic neoadjuvant response score (NAR). Serial MRIs were needed from 110 patients. Three radiologists independently, then collectively, reviewed each MRI for complete response (mriCR), which was tested for positive predictive value (PPV), negative predictive value (NPV), sensitivity, and specificity with pCR. MR-TRG was examined for association with the pathologic NAR score. All team members were blinded to pathologic data.

RESULTS

A total of 121 patients from 71 institutions met criteria: 28% were female (n = 34), 84% White (n = 101), and median age was 55 (24-78 years). Kappa scores for T- and N-stage after TNT were 0.38 and 0.88, reflecting fair agreement and near-perfect agreement, respectively. Calling an mriCR resulted in a kappa score of 0.82 after chemotherapy and 0.56 after TNT reflected near-perfect agreement and moderate agreement, respectively. MR-TRG scores were associated with pCR (P < .01) and NAR (P < .0001), PPV for pCR was 40% (95% CI, 26 to 53), and NPV was 84% (95% CI, 75 to 94).

CONCLUSION

MRI alone is a poor tool to distinguish pCR in rectal adenocarcinoma undergoing TNT. However, the MR-TRG score presents a now validated method, correlated with pathologic NAR, which can objectively measure regression magnitude during TNT.

Abstract P1-04-10: Association of stromal tumor infiltrating lymphocytes (sTILs) in pretreatment biopsies in different molecular subtypes of HER2+/ER+ breast cancer: Assessment of NRG Oncology/NSABP B-52

Background: The primary aim of the NRG Oncology/NSABP B-52 clinical trial was to test if estrogen deprivation (ED) administered concomitantly with neoadjuvant docetaxel, carboplatin, trastuzumab, and pertuzumab (TCHP), would improve the pCR rate in patients with HER2+/ER+ early breast cancer. A numerical increase in the pCR rate was observed with ED (46.1% v 40.9%), but the difference was not statistically significant. The purposes of this study were to assess the association of sTILs in pretreatment biopsies with pCR in the total population and within the molecular subtypes of breast cancer and to assess changes in sTILs between pre- and on-treatment biopsies. The secondary endpoints of recurrence-free interval (RFI) and overall survival (OS) are currently being analyzed and will be presented along with association of these endpoints with sTILs in pretreatment biopsies in the total cohort and within molecular subtypes. Methods: Scoring of sTILs on routine H&E slides from pre-treatment biopsies with sufficient tumor from 249 of the 315 patients (79%) entered in B-52 were performed by one of two pathologists (SKM, RSM). Both pathologists scored sTILs on a subset of 64 patients to document concordance. Wilcoxon two-sided test, box and whisker plots, and forest plots were used to assess associations with pCR. Molecular subtypes were determined utilizing RNA-seq data and AIMS subtyping method. On-treatment biopsies were available in 46 patients and were scored and compared to paired baseline samples. Results: Good concordance between pathologists was established with an inter-pathologist difference of ˂20% difference between scores in 92% of cases. sTILs in pre-treatment samples were associated with pCR across both arms of the trial (p=0.0074) and in the TCHP+ED arm (p=0.033), but not in the TCHP arm (p=0.093). The distribution of intrinsic subtypes was 34% luminal B, 29% luminal A, 28% HER2E, 5.8% normal, and 2.7% basal, with no significant differences between the arms. Presence of sTILs showed a trend for association with pCR in HER2E pre-treatment samples (p=0.054) but not in non-HER2E (p=0.75). Similarly, sTILs were associated with pCR in non-luminal tumors (p=0.055) but not in luminal tumors (p=0.44). Stratification by treatment arm and menopausal status suggested sTILs are associated with pCR in premenopausal women treated with TCHP (OR: 1.04, 95% CI=1.00-1.09). Interestingly, decreases in the sTIL scores with treatment were associated with pCR in the TCHP+ED arm (p=0.01) but not in the TCHP arm. Analysis of RFI and OS on B-52 is ongoing and will be presented along with associations of sTILs with intrinsic subtypes for RFI and OS. Conclusions: Although a positive correlation between sTILs and pCR was observed, the clinical utility appears limited because of the extensive overlap in the TIL scores between pCR and non-pCR tumors. Significance for a positive association of sTILs with pCR was detected in HER2E but not in luminal tumors. This may be due to the molecular differences of the subtypes, or the make-up of the TILs, or both. The association of a decrease in sTILs with TCHP+ED treatment needs further investigation. The small number of samples is a limitation of the study; however, the B-52 protocol specified that the collection of the B-52 samples was for the purpose of exploratory analysis. Our results highlight the molecular heterogeneity of the HER+/ER+ patient population and suggests that different treatment strategies may be required in future treatment regimens for this patient population. Support: NSABP Foundation; BCRF; 3U10CA180868-03S2, -180822; UG1CA189867; Genentech.

Citation Format: Katherine L. Pogue-Geile, Sai K. Maley, Rim S. Kim, Ying Wang, Roberto Salgado, Corey Lipchik, Huichen Feng, Reena S. Cecchini, Samuel A. Jacobs, Ashok Srinivasan, Eleftherios (Terry) Mamounas, Charles E. Geyer Jr, Priya Rastogi, C. Kent Osborne, Soonmyung Paik, Norman Wolmark, Peter C. Lucas, Mothaffar Rimawi. Association of stromal tumor infiltrating lymphocytes (sTILs) in pretreatment biopsies in different molecular subtypes of HER2+/ER+ breast cancer: Assessment of NRG Oncology/NSABP B-52 [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P1-04-10.

NRG-GI004/SWOG-S1610: Colorectal Cancer Metastatic dMMR Immuno-Therapy (COMMIT) study—A randomized phase III study of atezolizumab (atezo) monotherapy versus mFOLFOX6/bevacizumab/atezo in the first-line treatment of patients (pts) with deficient DNA mismatch repair (dMMR) or microsatellite instability high (MSI-H) metastatic colorectal cancer (mCRC)

TPS258

Background: Despite the superiority in progression-free survival (PFS) of inhibition of programmed cell death-1 (PD-1) pathway in dMMR/MSI-H as compared to chemotherapy with either anti-vascular endothelial growth factor receptor (VEGFr) or anti-epithelial growth factor receptor (EGFr) antibodies in mCRC, more pts had progressive disease as the best response in the anti-PD1 monotherapy arm (29.4% v 12.3%) with mean PFS of 13.7 mos, with ~45% of pts in the immunotherapy arm progressed at 12 mos (KEYNOTE 177). We hypothesize that dMMR/MSI-H mCRC pts may be more effectively treated with the combination of PD-1 pathway blockade and mFOLFOX6/bevacizumab (bev) rather than with anti-PD-1 therapy (atezo) alone. Preclinical work demonstrated synergistic effects between anti-PD-1/anti-VEGF and between oxaliplatin/anti-PD-1 in murine CRC models and phase II data, which showed activity of anti-PD-1/anti-VEGF in chemotherapy refractory colon cancer. A recent randomized trial subgroup analysis of 8 pts with dMMR metastatic colon cancer treated with FOLFOXIRI+bev+atezo, with the first patient having progression ~16 mos (AtezoTRIBE). Additionally, in other solid tumor malignancies, anti-PD1 plus anti-VEGFr (i.e., HCC and RCC) as well as anti-PD1 plus chemotherapy (i.e., gastric and esophageal cancers) combinations are standard first-line treatments. Methods: The redesigned COMMIT study was reactivated on 1/29/2021 as a two-arm prospective phase III open-label trial randomizing (1:1) mCRC dMMR/MSI-H to atezo monotherapy v mFOLFOX6/bev+atezo combination. Assuming our control arm, atezo monotherapy (48% PFS at 24 mos as assessed by site investigator), we have 80% power to detect a hazard ratio of 0.6 (equivalent to 64.4% PFS at 24 mos) with alpha 0.025 one-sided. Stratification factors include BRAFV600E status, metastatic site, and prior adjuvant CRC therapy. Secondary endpoints include OS, objective response rate, safety profile, disease control rate, and duration of response. Health-related quality of life is an exploratory objective. Archived tumor tissue and blood samples will be collected for correlative studies. Key inclusion criteria are: mCRC without prior chemotherapy for advanced disease; dMMR tumor determined by local CLIA-certified IHC assay (MLH1/MSH2/MSH6/PMS2) or MSI-H by local CLIA-certified PCR or NGS panel; and measurable disease per RECIST. Enrollment actively continues to the target accrual of 211 patients randomized between the two immunotherapy arms. Clinical trial: NCT02997228. Support: U10CA180868, -180822, -180888, UG1CA189867, U24CA196067; Genentech, Inc. Clinical trial information: NCT05080673 .

Phase II/III study of circulating tumor DNA as a predictive biomarker in adjuvant chemotherapy in patients with stage II colon cancer: NRG-GI005 (COBRA)

TPS259

Background: Detection of circulating tumor DNA (ctDNA) shed into the bloodstream represents a highly specific and sensitive approach for identifying microscopic or residual tumor cells after surgical resection. For patients (pts) with colon cancer (CC), the detection of ctDNA is associated with persistent disease after resection and outperforms traditional clinical and pathological features in prognosticating risk for recurrence. However, for pts with stage II CC, there are currently no validated biomarkers predicting benefit in identifying pts whose residual disease cancer be cleared by adjuvant chemotherapy. We hypothesize that for pts whose stage II colon cancer has been resected and who have no traditional high-risk features, a positive ctDNA status may identify those who will benefit from adjuvant chemotherapy. Methods: In this prospective phase II/III clinical trial, pts (N=1,408) with resected stage II CC without traditional high-risk features and whom the evaluating oncologist deems suitable for active surveillance (i.e., not needing adjuvant chemotherapy) will be randomized 1:1 into 2 arms: standard-of-care/observation (Arm A), or prospective testing for ctDNA (Arm B). Postoperative blood will be analyzed for ctDNA with the Guardant Reveal assay, covering CC-relevant mutations and CC-specific methylation profiling. Pts in Arm B with ctDNA detected will be treated with 6 months of adjuvant (FOLFOX) chemotherapy. For all pts in Arm A, ctDNA status will be analyzed retrospectively at the time of endpoint analysis. The primary endpoints are clearance of ctDNA with adjuvant chemotherapy (phase II) and recurrence-free survival (RFS) for “ctDNA-detected” pts treated with or without adjuvant chemotherapy (phase III). Secondary endpoints will include time-to-event outcomes (OS, RFS, TTR) by ctDNA marker status and treatment, prevalence of detectable ctDNA in stage II CC, and rates of compliance with assigned intervention. Archived normal and matched tumor and blood samples will be collected for exploratory correlative research. Enrollment continues across North America to the 540-patient phase II endpoint. Support: U10CA180868, -180822; UG1CA189867; GuardantHealth. Clinical trial information: NCT04068103 .

A flexible proton beam imaging energy spectrometer (PROBIES) for high repetition rate or single-shot high energy density (HED) experiments (invited)

The PROBIES diagnostic is a new, highly flexible, imaging and energy spectrometer designed for laser-accelerated protons. The diagnostic can detect low-mode spatial variations in the proton beam profile while resolving multiple energies on a single detector or more. When a radiochromic film stack is employed for "single-shot mode," the energy resolution of the stack can be greatly increased while reducing the need for large numbers of films; for example, a recently deployed version allowed for 180 unique energy measurements spanning ∼3 to 75 MeV with <0.4 MeV resolution using just 20 films vs 180 for a comparable traditional film and filter stack. When utilized with a scintillator, the diagnostic can be run in high-rep-rate (>Hz rate) mode to recover nine proton energy bins. We also demonstrate a deep learning-based method to analyze data from synthetic PROBIES images with greater than 95% accuracy on sub-millisecond timescales and retrained with experimental data to analyze real-world images on sub-millisecond time-scales with comparable accuracy.

Long-term results from NRG-GI002: A phase II clinical trial platform using total neoadjuvant therapy (TNT) in locally advanced rectal cancer (LARC)

7

Background: This NCTN multi-arm randomized phase II modular clinical trial platform utilizes TNT with parallel experimental arms (EAs) in LARC. EAs are not intended for direct comparison, but rather to concurrently randomized control arm (CA) patients. Primary endpoint (EP) and available secondary EPs (from EA1 using veliparib [V], PARPi; and EA2 using pembrolizumab [P], anti-PD-1) have been previously reported. We present long-term outcomes of all pts enrolled (NCT02921256). Methods: Stage II/III pts with MSS LARC (with any ONE of the following: distal location [cT3-4 ≤5cm from anal verge, any N]; bulky [any cT4 or tumor within 3mm of mesorectal fascia]; high risk for metastatic disease [cN2]; or not a sphincter-sparing surgery [SSS] candidate) were randomized to CA (neoadjuvant FOLFOX [x 4mo] → chemoRT [capecitabine with 50.4Gy] → surgery 8-12 wks later). EA1 added V (400mg PO BID) and EA2 added P (200mg IV Q3 wks x 6 doses) each concurrent with chemoRT. Primary EP: 4-point reduction in Neoadjuvant Rectal Cancer (NAR) score with a one-sided α=0.10, 80% power. NAR compared by linear model controlling for clinical T4 at entry (Y/N). Secondary EPs: OS, DFS. p-values are two-sided. Results: From 10/2016-2/2018, 178 pts were randomized (88 CA, 90 EA1). From 8/2018-5/2019, 185 pts were randomized (95 CA, 90 EA2). Baseline characteristics were previously reported. Median follow-up is 3.50 yrs for the 1st comparison. Median follow-up is 3.15 yrs for the 2nd comparison. Updated primary and long-term secondary outcomes are in the table. Conclusions: With longer follow-up, addition of V to TNT provided no significant differences in the NAR score or 3yr outcomes. The addition of P to TNT was associated with a statistically significant improvement in 3yr OS, but not DFS. Correlative molecular analyses are ongoing. Support: U10CA180868, -180822; UG1-189867; U24-196067; AbbVie; Merck. Clinical trial information: NCT02921256 . [Table: see text]

NRG GI008: Colon adjuvant chemotherapy based on evaluation of residual disease (CIRCULATE-US)

TPS260

Background: Currently, there are no biomarkers validated prospectively in randomized studies for resected colon cancer (CC) to determine need for adjuvant chemotherapy (AC). However, circulating tumor DNA (ctDNA) represents a highly specific and sensitive approach (especially with serial monitoring) for identifying minimal/molecular residual disease (MRD) post-surgery in CC patients (pts), and may outperform traditional clinical and pathological features in prognosticating risk for recurrence. CC pts who do not have detectable ctDNA (ctDNA-) are at a much lower risk of recurrence and may be spared the toxicities associated with AC. Furthermore, for CC pts with detectable ctDNA (ctDNA+) who are at a very high risk of recurrence, the optimal AC regimen has not been established. We hypothesize that for pts whose CC has been resected, ctDNA status may be used to risk-stratify for making decisions about AC. Methods: In this prospective phase II/III trial, up to 1,912 pts with resected stage III A, B (all pts) and stage II, IIIC (ctDNA+ only) CC will be enrolled. Based on the post-operative ctDNA status using personalized and tumor-informed assay (Signatera™, bespoke assay), those who are ctDNA- (Cohort A) will be randomized to immediate AC with fluoropyrimidine (FP) + oxaliplatin (Ox) for 3-6 mos per established guidelines vs . serial ctDNA monitoring. Patients who are ctDNA+ post-operatively or with serial monitoring (Cohort B) will be randomized to FP+Ox vs . more intensive AC with addition of irinotecan (I) for 6 mos. The primary endpoints for Cohort A are time to ctDNA+ status (phase II) and disease-free survival (DFS) (phase III) in the immediate vs . delayed AC arms. The primary endpoint for Cohort B is DFS in the FP+Ox vs FP+Ox+I arms for both phase II and phase III portions of the trial. Secondary endpoints include prevalence of detectable ctDNA post-operatively, time-to-event outcomes (overall survival and time to recurrence) by ctDNA status, and the assessment of compliance to adjuvant therapy. Biospecimens including archival tumor tissue, as well as post-operative plus serial matched/normal blood samples, will be collected for exploratory correlative research. Active enrollment across the NCTN started in June, 2022. Support: U10-CA-180868, -180822; UG1CA-189867; Natera, Inc. Clinical trial information: NCT05174169 .

NSABP FC-11: A phase II study of neratinib (N) plus trastuzumab (T) or N plus cetuximab (C) in patients (pts) with "quadruple wild-type" metastatic colorectal cancer (mCRC) based on HER2 status

3564

Background: Patients (pts) with KRAS wild-type (WT) mCRC treated with single agent anti-EGFR therapy (tx) have improved OS compared to BSC but only a 10-15% response rate. Prior EGFR tx may upregulate HER amplification. For pts with quadruple WT mCRC (KRAS, NRAS, BRAF, PIC3KA), data suggest that dual targeting of the MAPK pathway, specifically EGFR and HER2, may be more effective. The purpose of this study was to evaluate the activity of dual MAPK pathway inhibition based on HER2 status: amplified (amp), non-amplified (non-amp), or mutated (mt). Methods: This 2-arm phase II trial enrolled pts with quad WT mCRC with ECOG PS 0-2, adequate organ function, prior oxaliplatin- and irinotecan-based regimens, and known HER2 status. Arm 1: HER2 amp (confirmed as >2.14 copy number by Guardant 360) and prior anti-EGFR tx or HER2 mt (with qualifying mt) with or without prior anti-EGFR tx; Arm 2: HER2 non-amp or HER2 amp without prior anti-EGFR tx. Tx included T 4 mg/kg IV loading dose → 2 mg/kg/wk and N 240 mg po daily (Arm 1) or C 400 mg/m2 IV loading dose → 250 mg/m2/wk and N 240 mg po daily (Arm 2). Imaging was performed every 8 wks with response per RECIST 1.1. Primary end point (EP) of each arm was 6 mo PFS (PFS6). Secondary EPs: Response rate (ORR), clinical benefit rate (CBR), toxicity and exploratory assessments of N pharmacokinetics, genetic and molecular analyses, and evaluation of multiple drug combinations in PDX/PDXO models. We tested H0: PFS6 <0.13 v HA: PFS6 >0.47 (α=0.05; power=0.90 to reject HA). Treating 15 pts in each arm, if ≥5 pts are alive and progression free (PFS6 0.33), the arm is worth further testing. Results: From Jul 2018 - Mar 2021, 25 pts enrolled from 9 different centers. Arm 1 closed due to poor accrual (n=4). Those pts have been excluded from further analysis. Arm 2 enrolled 21 pts. with 15 evaluable for response by imaging. Early discontinuation occurred in 6 of 21 pts: 2 withdrew consent, 3 due to toxicity, and 1 physician withdrawal. Of the 15 evaluable pts, there were 6 PR, 5 of 13 HER2 non-amp, 1 of 2 HER2 amp, (duration 120-171 days; mean 140) and 5 SD (duration 59-231 days; mean 124). The ORR (CR/PR) in all pts who received at least one dose of tx is 33% (6/20). 8 of 15 evaluable pts (53%) were progression free at cycle 6. Common grade 3+ AEs (>5%) included diarrhea (24%), rash (8%), and abdominal pain/distension (8%), without any grade 5 AEs. Conclusions: The combination of C+N was reasonably well tolerated with expected toxicities of diarrhea and rash. The ORR, CBR, and PFS compare favorably to pts previously relapsed following oxaliplatin and irinotecan and treated with single-agent anti-EGFR tx. Upon entry, biopsies for PDX implantation had an engraftment success rate of ̃80%. We anticipate using these grafts to establish PDXO models for molecular analyses and further drug testing. Support: NSABP Foundation, Puma Biotechnology. Clinical trial information: NCT03457896.

Colon adjuvant chemotherapy based on evaluation of residual disease (CIRCULATE-US): NRG-GI008

TPS3643

Background: Currently, there are no biomarkers validated prospectively in randomized studies for resected colon cancer (CC) to determine need for adjuvant chemotherapy (AC). However, circulating tumor DNA (ctDNA) represents a highly specific and sensitive approach (especially with serial monitoring) for identifying minimal/molecular residual disease (MRD) post-surgery in CC patients (pts), and may outperform traditional clinical and pathological features in prognosticating risk for recurrence. CC pts who do not have detectable ctDNA (ctDNA-) are at a much lower risk of recurrence and may be spared the toxicities associated with AC. Furthermore, for CC pts with detectable ctDNA (ctDNA+) who are at a very high risk of recurrence, the optimal AC regimen has not been established. We hypothesize that for pts whose CC has been resected, ctDNA status may be used to risk stratify for making decisions about AC. Methods: In this prospective phase II/III trial, up to 1,912 pts with resected stage III A, B (all pts) and stage II, IIIC (ctDNA+ only) CC will be enrolled. Based on the post-operative ctDNA status using personalized and tumor informed assay (SignateraTM, bespoke assay), those who are ctDNA- (Cohort A) will be randomized to immediate AC with fluoropyrimidine (FP) + oxaliplatin (Ox) for 3-6 mos per established guidelines vs . serial ctDNA monitoring. Patients who are ctDNA+ post-operatively or with serial monitoring (Cohort B) will be randomized to FP+Ox vs . more intensive AC with addition of irinotecan (I) for 6 mos. The primary endpoints for Cohort A are time to ctDNA+ status (phase II) and disease-free survival (DFS) in phase III in the immediate vs . delayed AC arms. The primary endpoint for Cohort B is DFS in the FP+Ox vs FP+Ox+I arms for both phase II and phase III portions of the trial. Secondary endpoints include prevalence of detectable ctDNA post-operatively, time-to-event outcomes (overall survival and time to recurrence) by ctDNA status, and the assessment of compliance to adjuvant therapy. Biospecimens including archival tumor tissue, post-operative and serial matched/normal blood samples will be collected for exploratory correlative research. Active enrollment across the NCTN started in early 2022. Support: U10-CA-180868, -180822; UG1CA-189867; Clinical trial information: NCT05174169.

NSABP FC-12: A single-arm, phase II study to evaluate treatment with gevokizumab in patients with stage II/III colon cancer who remain ctDNA+ after curative surgery and adjuvant chemotherapy

TPS3642

Background: Detection of circulating tumor DNA (ctDNA) in patients (pts) following surgery is indicative of presence of minimal/molecular residual disease (MRD) and confers a near-certain risk of disease recurrence. Therapeutic strategies to treat MRD following standard curative therapies are needed because the risk of recurrence is high and therapeutic intervention may provide clinical benefit to patients. Gevokizumab is a recombinant humanized monoclonal antibody targeting interleukin-1β (IL-1β), which is involved in all phases of the malignant process (tumorigenesis, invasion, metastasis, angiogenesis, progression, and the modulation of anti-tumor immunity). Gevokizumab has been validated in pre-clinical colon cancer (CC) models and safety established in the advanced-stage clinical setting. In this trial in progress, we aim to test the efficacy of gevokizumab in pts with early-stage CC with MRD (ctDNA-positivity) following definitive treatment. Methods: NSABP FC-12 is a single-arm, multi-centered phase II study that will include pts with stage II/III CC who test MRD+ within 6 wks following completion of curative surgery and ≥3 mos of adjuvant chemotherapy. MRD will be assessed using a personalized and tumor-informed ctDNA assay (Signatera bespoke assay). Gevokizumab will be given at a flat dose of 120 mg IV every 28 days for 13 cycles. The primary endpoint is relapse-free survival (RFS) following initiation of study therapy through one year of follow-up. Secondary endpoints are rate of ctDNA clearance at 8 wks from start of study therapy, as well as safety, toxicity, pharmacokinetics, and immunogenicity of gevokizumab. Exploratory and correlative endpoints will include outcomes associated with ctDNA clearance kinetics, tumor mutations, tumor mutational burden, circulating methylated DNA, tumor immune microenvironment profile, peripheral blood immune profile, and stool microbiome analyses. The enrollment period will be ̃12 mos. Pts will be followed for 18 mos following enrollment with ctDNA analysis at prespecified timepoints until imaging is positive for recurrence of disease or death. CT scans will be at 6-mo intervals. RFS will be determined in pts who clear ctDNA at 8 wks compared to those who do not. A single-stage design to test the null hypothesis that the 12-mo RFS is P≥0.20 versus the alternative (HA) that P≥0.35 has a sample size of 31 (alpha=0.151; power 0.811). If ≥9 of 31 pts (29%) are alive and recurrence-free at 12 mos, then gevokizumab will be considered promising for further study. Enrollment continues towards the primary endpoint. Clinical trial information: 05178576.

Colorectal cancer metastatic dMMR immuno-therapy (COMMIT) study: A randomized phase III study of atezolizumab (atezo) monotherapy versus mFOLFOX6/bevacizumab/atezo in the first-line treatment of patients (pts) with deficient DNA mismatch repair (dMMR) or microsatellite instability high (MSI-H) metastatic colorectal cancer (mCRC)—NRG-GI004/SWOG-S1610

TPS3647

Background: Despite the superiority in progression-free survival (PFS) of inhibition of programmed cell death-1 (PD-1) pathway in dMMR/MSI-H as compared to chemotherapy with either anti-vascular endothelial growth factor receptor (VEGFr) or anti-epithelial growth factor receptor (EGFr) antibodies in mCRC, more pts had progressive disease as the best response in the anti-PD1 monotherapy arm (29.4% v 12.3%) with mean PFS of 13.7 mos, with ̃45% of pts in the IO arm progressed at 12 mos ( N Engl J Med 2020; 383:2207). We hypothesize that the dMMR/MSI-H mCRC pts may be more effectively treated with the combination of PD-1 pathway blockade and mFOLFOX6/bevacizumab (bev) rather than with anti-PD-1 therapy (atezo) alone. Preclinical work demonstrated synergistic effects between anti-PD-1/anti-VEGF and between oxaliplatin/anti-PD-1 in murine CRC models and phase II data, which showed activity of anti-PD-1/anti-VEGF in chemotherapy refractory colon cancer. A recent randomized trial subgroup analyses of 8 pts with dMMR metastatic colon cancer treated with FOLFOXIRI+bev+atezo, with the first patient having progression ̃16 mos ( ESMO 2021, Abstt LBA20). Additionally, in other solid tumor malignancies, anti-PD1 plus anti-VEGFr (i.e., HCC and RCC) as well as anti-PD1 plus chemotherapy (i.e., gastric and esophageal cancers) combinations are standard first-line treatments. Methods: The redesigned COMMIT study was reactivated on 1/29/2021 as a two-arm prospective phase III open-label trial randomizing (1:1) mCRC dMMR/MSI-H to atezo monotherapy v mFOLFOX6/bev+atezo combination. Assuming our control arm, atezo monotherapy (48% PFS at 24 mos as assessed by site investigator), we have 80% power to detect a hazard ratio of 0.6 (equivalent to 64.4% PFS at 24 mos) with alpha 0.025 one-sided. Stratification factors include BRAFV600E status, metastatic site, and prior adjuvant CRC therapy. Secondary endpoints include OS, objective response rate, safety profile, disease control rate, and duration of response. Health-related quality of life is an exploratory objective. Archived tumor tissue and blood samples will be collected for correlative studies. Key inclusion criteria are: mCRC without prior chemotherapy for advanced disease; dMMR tumor determined by local CLIA-certified IHC assay (MLH1/MSH2/MSH6/PMS2) or MSI-H by local CLIA-certified PCR or NGS panel; and measurable disease per RECIST. Enrollment actively continues to the target accrual of 211 patients randomized between the two immunotherapy arms. Support: U10CA180868, -180822, -180888, UG1CA189867, U24CA196067. Clinical trial information: NCT02997228.

NSABP FC-10: A phase Ib study of pembrolizumab (pembro) in combination with pemetrexed (pem) and oxaliplatin (oxali) in patients with chemo-refractory metastatic colorectal cancer (mCRC)

3569

Background: Most pts with mCRC have microsatellite stable (MSS) disease (95%) which is unresponsive to checkpoint inhibition. Chemotherapy activity is mediated through both cytotoxicity as well as immunological effects including reduced T-regulatory cell activity, enhanced tumor antigen presentation, and induced PD-L1 tumor cell expression. Chemotherapy with checkpoint inhibitors can potentially activate T cells and alter the microenvironment to improve outcomes. Our purpose was to evaluate pembro plus pem in a safety run-in (cohort 1) and the same with dose-escalated oxali (cohort 2). Methods: Eligible pts with MSS mCRC had ECOG PS of 0-1, measurable metastatic disease, adequate organ function, and prior treatment with fluoropyrimidine-, oxali-, and irinotecan-based therapies (plus an anti-EGFR agent, if apropos). Cohort 1 treatment was pem 500 mg/m2 IV plus pembro 200 mg IV every 3 wks. Cohort 2 treatment was the same, plus oxali at an escalating dose of 85-120 mg/m2 utilizing a 3+3 design with expansion of 6 additional pts at the RP2D. Imaging was performed every 3 cycles; response was determined by RECIST 1.1. Primary endpoint (EP) of each cohort: safety and best ORR with cohort 2 also to establish the RP2D. Secondary EPs: Clinical benefit rate (CBR), PFS, OS at 1 year, and exploratory assessments of circulating immunologic profiles and molecular predictors of response. Descriptive statistics were planned as a signal-seeking study. Results: From Jul 2019-Apr 2021, 34 pts enrolled from 4 different centers. In cohort 1 (n=15), one pt was taken off study due to LFT elevation and orchitis attributed to pembro with reduced lymphadenopathy upon withdrawal. There was 1 PR (duration 686 days) and 4 SDs (61, 66, 124, 128 days) among 11 evaluable for response. There were no unexpected nor grade 5 toxicities. In cohort 2 (n=19), 2 pts achieved a PR (127 and 185 days), with SDs in 5 (59, 63, 69, 115, 437), among 13 evaluable for response. At oxali dose of 85 mg/m2, 1/6 pts had DLT (grade 4 neutropenia ≥7 days); another 1/6 pts had DLT at 120 mg/m2 (grade 3 AST/ALT). The RP2D was 120 mg/m2. Common grade 3/4 AEs included: neutropenia (24%), anemia (9%), fatigue (9%), abdominal pain (6%), nausea (6%), and ALT/AST (6%). There was no febrile neutropenia nor any grade 5 events. Combined cohort rates of PR/CBR were 3/24 (12.5%) and 12/24 (50%), respectively. Conclusions: In this study of heavily pretreated pts with MSS mCRC, combining pembro plus pem or pem+oxali was well tolerated. Overall CBR was 50%, with objective responses (PRs) in 3/24 (12.5%) evaluable pts. This compares favorably with KEYNOTE 016, in which pembro in MSS mCRC pts had 0/18 objective responses and CBR=11% (2/18). Further studies testing these agents in earlier lines of treatment with robust correlative analyses is supported. Support: NSABP Foundation; Merck; Lilly. Clinical trial information: NCT03626922.

Abstract PD15-03: Overlapping molecular features (proliferation, immune signatures andTP53mutations) associated with palbociclib resistance inER+HER2- primary breast cancer

Background: Cyclin-dependent kinase 4/6 (CDK4/6) inhibitors in combination with anti-hormone therapy are highly effective treatments for oestrogen receptor positive (ER+) and HER2 negative (HER2-) advanced breast cancer. Pre-clinical and clinical studies have reported mechanisms of resistance to CDK4/6 inhibitors to include interferon signalling, high CCNE1 expression and loss of RB1 expression. The PALLET phase II randomized neoadjuvant trial of letrozole (LET) ± palbociclib (PALBO) in postmenopausal ER+HER2- primary breast cancer showed that suppression of proliferation as measured by Ki67 was significantly greater with addition of PALBO to LET but did not result in all patients achieving complete cell-cycle arrest, indicating intrinsic resistance in some patients. We report phenotypes/genotypes associated with that resistance. Methods: In the PALLET trial, 307 patients were randomized to LET+PALBO (n=204) or LET (n=103) for 14wks. For the first 2wks of LET+PALBO patients were randomised to LET, PALBO or LET+PALBO. RNA-seq of baseline samples from consented patients was performed on fresh frozen biopsies for 224 patients (LET-only n=77; LET+PALBO n=147); whole exome sequencing was performed on 188 tumors and matched blood samples (LET-only n=61; LET+PALBO n=127). After 14wks of treatment, those patients with Ki67% &lt; 2.7% were classified as having complete cell-cycle arrest (CCCA). Differentially expressed genes (DEGs) were identified between patients sensitive (CCCA) and resistant (non-CCCA) to treatments with or without PALBO at 14wks by DESeq2. Mutect2 and VarScan was used to identify somatic mutations and CNVkit was used to identify copy number alterations in whole exome sequencing (WES). Results: In LET+PALBO treated patients, higher expression of E2F targets, interferon gamma response and mTORC1 signalling genes were observed in baseline gene expression of non-CCCA patients at 14wks (FDR&lt;0.05, GSEA). Similar results were also observed if using 2wk Ki67 data. In LET-only non-CCCA patients, higher expression of mTORC1 signalling and lower expression of oestrogen response genes (FDR&lt;0.05, GSEA) were observed. Additional analysis of baseline gene expression for non-CCCA at 14wks LET+PALBO patients showed higher expression of immune checkpoint inhibition associated genes including IFNG, IDO1, PD-L1 (FDR&lt;0.05, DESeq2), higher expression of genes expressed only in immune cells and two gene signatures related to interferon signalling and immune checkpoint blockade (FDR&lt;0.05, GSEA). Somatic mutation analysis showed a trend for enrichment of mutations in TP53 for both LET-only and LET+PALBO non-CCCA patients (p=0.02 and p=0.06, respectively, Fisher-exact) and significant enrichment of MAP3K1 mutations in LET-only CCCA patients (p&lt;0.05, Fisher-exact). TP53 mutations were also associated with higher proliferation, mTORC1 and immune related signatures (all p&lt;0.01, Mann-Whitney). Change at 14wks Ki67 was significantly different (p=0.02, Mann-Whitney) between TP53wt and TP53MUT for LET-only patients (median WT = -92%, MUT = -66%, p=0.02, Mann-Whitney ) but not for LET+PALBO (median WT = -99% MUT = -95%, p=0.13, Mann-Whitney). No copy number alterations were significantly enriched in LET+PALBO non-CCCA patients. Conclusion: We observe, confirming previous studies, an association of CDK4/6 inhibitor resistance, high expression of CCNE1 and genes related to interferon gamma signalling. We show that there is an overlap between resistance mechanisms and TP53 mutations. However, ER+HER2- patients with TP53 mutations may still benefit from PALBO adding to suppression of proliferation compared to LET-only treatment.

Citation Format: Eugene F Schuster, Hui Xiao, Maggie Cheang, Elena Lopez-Knowles, Lucy Kilburn, Viktoriya Korchina, Sejal Salvi, Samuel A Jacobs, Melanie Finnigan, David A Wheeler, Shannon Puhalla, Donna Muzny, Harsha Doddapaneni, Katherine Pogue-Geile, Yuan Liu, Judith Bliss, Stephen Johnston, Mitch Dowsett, Mothaffar Rimawi, On behalf of the PALLET Trialists. Overlapping molecular features (proliferation, immune signatures andTP53mutations) associated with palbociclib resistance inER+HER2- primary breast cancer [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr PD15-03.

Abstract P1-07-04: Potential role of the antibody-dependent cellular phagocytosis (ADCP) in tumors achieving pCR in NRG Oncology/NSABP B-52

Background: The NRG Oncology/NSABP B-52 neoadjuvant clinical trial was conducted to test if the addition of estrogen deprivation (ED) would improve the pCR rate in HER2+/ER+ breast cancer patients (pts) treated with docetaxel, carboplatin, trastuzumab, and pertuzumab (TCHP). A numerical increase in pCR rate was observed with ED (46.1% v 40.9%), but the difference was not statistically significant. We have previously quantitated T cells (CD8, FOXP3), macrophages (CD68), and immune checkpoint proteins (PD-1, PD-L1) with multiplex immunofluorescence in B-52 and shown that CD68 and FOXP3 cells were associated with pCR but not CD8 cells. Our purpose was to determine the associations of FCGR genotypes and immune cells with pCR. Methods: A single baseline, pre-treatment FFFPE tissue section per case (N=181) was used to perform a 7-plex multiplex immunofluorescence procedure using opal fluorophores for staining. The Vectra Pathology System and inForm analysis software (Akoya Biosciences) was used for imaging and quantitation of CD8, CD68, FOXP3, PD-1, and PD-L1 cells in both the tumoral and stromal regions. Stromal data is reported here. Favorable- and unfavorable- FcGγR genotypes for FCGR2A-131H/R and FCGR3A-158V/F alleles were determined via the Sequenom MassARRAY iPLEX platform. Rates of pCR with pts with 1 or 2 favorable alleles was compared to pts who were homozygous for the unfavorable allele. Within each genotype, Wilcoxon rank sum test was used to test the association of markers with pCR and within each treatment. Results: No significant association of FCGR2A and 3A alleles with pCR was detected in the entire B-52 cohort, however, among pts with favorable FCGR genotypes (FCGR2A-131-HH, or H/R, FCGR3A-158- VV, or VF HR) the median value of the % CD68 cells was significantly higher in tumors that achieved pCR v those that did not (p=0.0004, p=0.0006), respectively. In pts who were homozygous for the FCGR2A or FCGR3A unfavorable alleles, there was no significant difference in the median values of the % of CD68 cells between pCR and no-pCR tumors. Further stratification of tumors by treatment showed that pts with an FCGR2A or FCGR3A favorable genotype and whose tumors achieved pCR had a higher median value of CD68 only in the TCHP + ED arm (p=0.0007, p=0.0003), respectively and not in the TCHP arm (p=0.059; p=0.21). Higher levels of PD-L1 were associated with pCR in pts with FCGR3A- favorable genotypes, but higher levels of FOXP3 were associated with pCR regardless of genotype. In contrast to the other cell types, higher PD-1 or CD8 cells showed no association with genotypes. Conclusions: This is an exploratory study examining the potential role of ADCP in HER2+/ER+ breast cancer and supports the notion that ADCP may be one mechanism that promotes the elimination of tumor cells in a subset of pts in the neoadjuvant setting. Tumors that achieve pCR have higher % of CD68 cells, in pts with favorable FCGR2A and 3A genotypes than pts who do not. However, in pts with unfavorable FCGR3A or FCGR2A genotypes there was no difference in the median CD68 levels in pCR v no-pCR tumors. When tumors were further stratified by CD68 levels, FCGR3A genotypes, and treatment, the association of pCR in tumors with high CD68 and FCGR3A favorable genotypes was seen only in the TCHP+ED arm. This may indicate that ED may improve pCR rates in some tumors with more macrophages and favorable genotypes. Macrophages are known to have estrogen receptors, and estrogen has been shown to promote the alternative activation of macrophages, potentially dampening down the immune response. Thus, one could speculate that ED may block the estrogen-induced alternative activation of macrophages, allowing the classically activated macrophages to phagocytize tumor cells. Support: BCRF, U10CA180868 & Admin Sup, U24CA196067, Genentech, NSABP Foun.

Citation Format: Katherine L Pogue-Geile, Ying Wang, Huichen Feng, Corey Lipchick, Patrick Gavin, Rim S Kim, Reena S Cecchini, Samuel A Jacobs, Ashok Srinivasan, Sandra M Swain, Eleftherios Mamounas, Charles E Geyer, Jr, Priya Rastogi, Peter C Lucas, C. Kent Osborne, Soonmyung Paik, Norman Wolmark, Mothaffar F Rimawi. Potential role of the antibody-dependent cellular phagocytosis (ADCP) in tumors achieving pCR in NRG Oncology/NSABP B-52 [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P1-07-04.

Association of multiplex-immunofluorescence (m-IF) and gene expression signature with prognosis and bevacizumab (bev) treatment outcomes in NRG oncology/NSABP C-08: Implications for combining immune checkpoint blockade (ICB) and bev

140

Background: NRG Oncology/NSABP C-08 tested the efficacy of adding bev to mFOLFOX in patients (pts) with stage II or III colon cancer. In an unplanned analysis we showed that MMR status was predictive of bev benefit with dMMR pts receiving statistically significant bev benefit. More recently, we showed that immune cells and immune checkpoint proteins have differential effects on prognosis and bev benefit in C-08 (ASC0 2021). As part of a preplanned secondary objective of an NCTN-CCSC approved protocol, we tested the association of VEGFR, VEGFA, and CD31, with clinical outcomes and treatment benefit in dMMR and pMMR pts enrolled in C-08. To determine what subset of pts within C-08 received bev benefit, we tested the 10-gene IFNɣ signature (Ayers et al 2017), which has been shown to associate with response to ICB in other studies. Methods: VEGFR, VEGFA, and CD31 were quantitated in tumors from C-08 pts (N=1,485) using m-IF and the Vectra Pathology System and inForm software. Gene expression data of C-08 (n=387) via DASLR microarrays was used to test the IFNɣ signature for association with bev benefit in dMMR and pMMR pts. All markers were tested for associations with prognosis and bev benefit in dMMR and pMMR pts using recurrence-free interval, median cut points, and Cox models. Results: VEGFR, VEGFA, and CD31 were not prognostic in the total C-08 cohort nor in dMMR or pMMR subsets. However, high VEGFR was associated with bev benefit in dMMR pts p=0.0012, HR=0.08 [95% CI; 0.025-0.224], n=117) but not in pts with pMMR (n=555) (int p=0.03). Pts whose tumors showed higher expression of the IFNɣ signature had a better prognosis than did pts with a low signature. Importantly, in the entire C-08 cohort with available DASL data, pts with low IFNɣ signatures received bev benefit (p=0.034, HR=0.59 [95% CI: 0.36-0.97], n=211). When low IFNɣ tumors were further split by MMR status both dMMR and pMMR pts showed a trend to receive bev benefit, however, numbers of pts were too small to make firm conclusions (dMMR no bev vs. bev p=0.02, n=11; pMMR no bev vs. bev, p=0.051, n=167). Conclusions: High VEGFR is associated with bev benefit in dMMR pts. In agreement with other studies, we observe that the IFNɣ signature is associated with a good prognosis in C-08, however, unique to this study is the observation that IFNɣ low is associated with bev benefit in the entire C-08 cohort. The association of high IFNɣ signature with ICB response seen in several other studies, plus our observation that low IFNɣ is associated with bev benefit in C-08, suggests that bev and ICB are most efficacious on different subsets of pts. Current clinical trial, GI-004, is testing the efficacy of the bev + atezolizumab combination. Examination of these markers may be informative. Support: PA DOH, U10CA-180868, -180822, -196067, Genentech, Sanofi; NSABP Clinical trial information: 00096278.

Phase II/III study of circulating tumor DNA as a predictive biomarker in adjuvant chemotherapy in patients with stage II colon cancer: NRG-GI005 (COBRA)

TPS233

Background: There are currently no validated predictive biomarkers for stage II resected colon cancer (CC) after adjuvant chemotherapy. However, circulating tumor DNA (ctDNA) shed into the bloodstream represents a highly specific and sensitive approach for identifying microscopic or residual tumor cells. For patients (pts) with CC, the detection of ctDNA is associated with persistent disease after resection and may outperform traditional clinical and pathological features in prognosticating risk for recurrence. We hypothesize that for pts whose stage II colon cancer has been resected and who have no traditional high-risk features, a positive ctDNA status may identify those who will benefit from adjuvant chemotherapy. Methods: In this prospective phase II/III clinical trial, pts (N = 1,408) with resected stage II CC without traditional high-risk features and whom the evaluating oncologist deems suitable for active surveillance (i.e., not needing adjuvant chemotherapy) will be randomized 1:1 into 2 arms: standard-of-care/observation (Arm A), or prospective testing for ctDNA (Arm B). Postoperative blood will be analyzed for ctDNA with the Guardant Reveal assay, covering CC-relevant mutations and CC-specific methylation profiling. Pts in Arm B with ctDNA detected will be treated with 6 months of adjuvant (FOLFOX) chemotherapy. For all pts in Arm A, ctDNA status will be analyzed retrospectively at the time of endpoint analysis. The primary endpoints are clearance of ctDNA with adjuvant chemotherapy (phase II) and recurrence-free survival (RFS) for “ctDNA-detected” pts treated with or without adjuvant chemotherapy (phase III). Secondary endpoints will include time-to-event outcomes (OS, RFS, TTR) by ctDNA marker status and treatment, prevalence of detectable ctDNA in stage II CC, and rates of compliance with assigned intervention. Archived normal and matched tumor and blood samples will be collected for exploratory correlative research. Enrollment continues across North America to the 540-patient phase II endpoint. Support: U10-CA-180868, -180822; UG1CA-189867; GuardantHealth. Clinical trial information: NCT04068103.

Phase II study of durvalumab following neoadjuvant chemoRT in operable rectal cancer: NSABP FR-2

99

Background: Although immunotherapy shows no benefit in microsatellite stable (MSS) colorectal cancer, preclinical models suggest that radiotherapy (RT) can enhance neoantigen presentation, modulate the microenvironment, and improve the likelihood of anti-tumor activity with checkpoint inhibitor use. Using a “window-of-opportunity” study design, this prospective phase II trial will determine the safety and activity of this approach with the anti-PD-L1 agent durvalumab (MEDI4736). Methods: Stage II/III patients (pts) with MSS rectal cancer undergoing standard NCCN guideline-compliant neoadjuvant chemoradiotherapy (CRT) followed by definitive surgery were eligible. Treatment included durvalumab (750mg IV infusion once every 2 wks) for 4 total doses beginning within 3-7 days after CRT completion followed by surgery within 8-12 wks of the final CRT dose. Primary end point (EP): Improvement in modified neoadjuvant rectal cancer (mNAR) score (goal 10.6) compared to historical controls (15.6) targeting a 20% DFS RR reduction and 3-4% absolute OS improvement. Secondary EPs: toxicity, pCR, cCR, therapy completion, negative surgical margins, sphincter preservation, and exploratory assessments of tumor-infiltrating lymphocytes, tumor Immunoscore, circulating immunologic profiles, and molecular predictors of response. We test H0: mNAR ≥15.6 vs HA: mNAR <15.6 at alpha 0.10 one-sided with statistical significance defined as p<0.1. Results: From May 2018 to October 2020, 45 pts were enrolled with 40 pts evaluable for mNAR. Mean mNAR was 12.03 (80% CI: 9.29-14.97) (p=0.06 one-sided). pCR=22.2%; cCR=31.1%; R0 resection=81.0%, and sphincter preservation=71.4%. Side effects were consistent with both CRT and durvalumab safety profile. Most common grade 3 AEs included diarrhea, lymphopenia, and back pain. There was one grade 4 AE (elevated amylase/lipase) and no grade 5 AEs. Remaining secondary and correlative immunologic end points are still being assessed. Conclusions: Durvalumab immediately following CRT prior to surgery for definitive management of rectal cancer was safe and without unexpected short-term toxicities. The primary end point of mean mNAR score was significantly less than our historical control, warranting further investigation. Correlative analyses for immunologic markers of response including PD-(L)1 expression and Immunoscore are ongoing. NCT 03102047. Support: AstraZeneca-Medimmune, NSABP Foundation. Clinical trial information: NCT03102047.

NRG-GI008: Colon adjuvant chemotherapy based on evaluation of residual disease (CIRCULATE-US)

TPS212

Background: Currently, there are no biomarkers validated prospectively in randomized studies for resected colon cancer (CC) to determine need for adjuvant chemotherapy (AC). However, circulating tumor DNA (ctDNA) shed into the bloodstream represents a highly specific and sensitive approach (especially with serial monitoring) for identifying microscopic or residual tumor cells in CC patients (pts) and may outperform traditional clinical and pathological features in prognosticating risk for recurrence. CC pts who do not have detectable ctDNA (ctDNA-) are at a much lower risk of recurrence and may not need AC. Furthermore, for CC pts with detectable ctDNA (ctDNA+) who are at a very high risk of recurrence, the optimal AC regimen has not been established. We hypothesize that for pts whose colon cancer has been resected, ctDNA status may be used to risk stratify for making decisions about AC. Methods: In this prospective phase II/III trial, up to 1,912 pts with resected stage III A, B (all pts) and stage II, IIIC (ctDNA+ only) CC will be enrolled. Based on the post-operative ctDNA status using Natera’s Signatera assay, those who are ctDNA- (Cohort A) will be randomized to immediate AC with fluoropyrimidine (FP) + oxaliplatin (Ox) for 3-6 mos per established guidelines vs serial ctDNA monitoring. Patients who are ctDNA+ post-operatively or with serial monitoring (Cohort B) will be randomized to FP + Ox vs more intensive AC with addition of irinotecan (I) for 6 mos. The primary objectives for Cohort A are time to ctDNA+ status (phase II) and disease-free survival (DFS) in phase III in the immediate vs delayed AC arms. The primary objective for Cohort B is DFS in the FP + Ox vs FP + Ox + I arms for both phase II and phase III portions of the trial. Secondary objectives include prevalence of detectable ctDNA post-operatively, time-to event outcomes (overall survival & time to recurrence) by ctDNA status, and the assessment of compliance to adjuvant therapy. Biospecimens including archival tumor tissue, post-operative and serial matched/ normal blood samples will be collected for exploratory correlative research. Study will activate in early 2022 across the NCTN. NCT#: Pending. Support: U10-CA-180868, -180822; UG1CA-189867; Natera.

NRG-GI004/SWOG-S1610: Colorectal cancer metastatic dMMR immuno-therapy (COMMIT) study—A randomized phase III study of atezolizumab (atezo) monotherapy versus mFOLFOX6/bevacizumab/atezo in the first-line treatment of patients (pts) with deficient DNA mismatch repair (dMMR) or microsatellite instability high (MSI-H) metastatic colorectal cancer (mCRC)

TPS232

Background: Despite the superiority in progression-free survival (PFS) of inhibition of programmed cell death-1 (PD-1) pathway in dMMR/MSI-H as compared to chemotherapy with either anti-vascular endothelial growth factor receptor (VEGFr) or anti-epithelial growth factor receptor (EGFr) antibodies in mCRC, more pts had progressive disease as the best response in the anti-PD1 monotherapy arm (29.4% vs. 12.3%) with mean PFS of 13.7 months ( N Engl J Med 2020; 383:2207). We hypothesize that the dMMR/MSI-H mCRC pts may be more effectively treated by the combination of PD-1 pathway blockade and mFOLFOX6/bevacizumab (bev) rather than with anti-PD-1 therapy (atezo) alone. Preclinical work demonstrated synergistic effects between anti-PD-1/anti-VEGF and between oxaliplatin/anti-PD-1 in murine CRC models and phase II data showed activity of anti-PD-1/anti-VEGF in chemotherapy refractory colon cancer. Additionally, in other solid tumor malignancies, anti-PD1 plus anti-VEGFr (i.e., HCC and RCC) as well as anti-PD1 plus chemotherapy (i.e., gastric and esophageal cancers) combinations are standard first-line treatments. Methods: The redesigned COMMIT study was reactivated on 1/29/2021 as a two-arm prospective phase III open-label trial randomizing (1:1) mCRC dMMR/MSI-H (211 pts) to atezo monotherapy versus mFOLFOX6/bev+atezo combination. Assuming our control arm, atezo monotherapy, 48% PFS at 24 months, as assessed by site investigator, we have 80% power to detect a hazard ratio of 0.6 (equivalent to 64.4% PFS at 24 months) with alpha 0.025 one-sided. Stratification factors include BRAFV600E status, metastatic site, and prior adjuvant CRC therapy. Secondary endpoints include OS, objective response rate, safety profile, disease control rate, duration of response, and centrally-reviewed PFS. Health-related quality of life is an exploratory objective. Archived tumor tissue and blood samples will be collected for correlative studies. Key inclusion criteria are: mCRC without prior chemotherapy for advanced disease; dMMR tumor determined by local CLIA-certified IHC assay (MLH1/MSH2/MSH6/PMS2) or MSI-H by local CLIA-certified PCR or NGS panel; and measurable disease per RECIST. Enrollment actively continues to the target accrual of 211 patients randomized between the two immunotherapy arms. Support: U10CA180868, -180822, -180888, UG1CA189867, U24CA196067; Genentech, Inc. Clinical trial information: NCT02997228.

Biomarkers of Response and Resistance to Palbociclib Plus Letrozole in Patients With ER+/HER2- Breast Cancer

PURPOSE

To determine (i) the relationship between candidate biomarkers of the antiproliferative (Ki67) response to letrozole and palbociclib alone and combined in ER⁺/HER2^- breast cancer; and (ii) the pharmacodynamic effect of the agents on the biomarkers.

EXPERIMENTAL DESIGN

307 postmenopausal women with ER⁺/HER2^- primary breast cancer were randomly assigned to neoadjuvant treatment with letrozole for 14 weeks; letrozole for 2 weeks, then letrozole+palbociclib to 14 weeks; palbociclib for 2 weeks, then letrozole+palbociclib to 14 weeks; or letrozole+palbociclib for 14 weeks. Biopsies were taken at baseline, 2 and 14 weeks and surgery at varying times after stopping palbociclib. Immunohistochemical analyses were conducted for Ki67, c-PARP, ER, PgR, RB1, CCNE1, and CCND1.

RESULTS

Higher baselines ER and PgR were significantly associated with a greater chance of complete cell-cycle arrest (CCCA: Ki67 <2.7%) at 14 weeks and higher baseline Ki67, c-PARP, and CCNE1 with a lower chance. The interaction with treatment was significant only for c-PARP. CCND1 levels were decreased c.20% by letrozole at 2 and 14 weeks but showed a tendency to increase with palbociclib. CCNE1 levels fell 82% (median) in tumors showing CCCA but were unchanged in those with no CCCA. Only 2/9 tumors showed CCCA 3-9 days after stopping palbociclib. ESR1 mutations were found in 2/4 tumors for which surgery took place ≥6 months after starting treatment.

CONCLUSIONS

High CCNE1 levels were confirmed as a biomarker of resistance to letrozole+palbociclib. Ki67 recovery within 3-9 days of discontinuing palbociclib indicates incomplete suppression of proliferation during the "off" week of its schedule.

Use of Total Neoadjuvant Therapy for Locally Advanced Rectal Cancer: Initial Results From the Pembrolizumab Arm of a Phase 2 Randomized Clinical Trial

Importance

Total neoadjuvant therapy (TNT) is often used to downstage locally advanced rectal cancer (LARC) and decrease locoregional relapse; however, more than one-third of patients develop recurrent metastatic disease. As such, novel combinations are needed.

Objective

To assess whether the addition of pembrolizumab during and after neoadjuvant chemoradiotherapy can lead to an improvement in the neoadjuvant rectal (NAR) score compared with treatment with FOLFOX (5-fluorouracil, leucovorin, and oxaliplatin) and chemoradiotherapy alone.

Design, Setting, and Participants

In this open-label, phase 2, randomized clinical trial (NRG-GI002), patients in academic and private practice settings were enrolled. Patients with stage II/III LARC with distal location (cT3-4 ≤ 5 cm from anal verge, any N), with bulky disease (any cT4 or tumor within 3 mm of mesorectal fascia), at high risk for metastatic disease (cN2), and/or who were not candidates for sphincter-sparing surgery (SSS) were stratified based on clinical tumor and nodal stages. Trial accrual opened on August 1, 2018, and ended on May 31, 2019. This intent-to-treat analysis is based on data as of August 2020.

Interventions

Patients were randomized (1:1) to neoadjuvant FOLFOX for 4 months and then underwent chemoradiotherapy (capecitabine with 50.4 Gy) with or without intravenous pembrolizumab administered at a dosage of 200 mg every 3 weeks for up to 6 doses before surgery.

Main Outcomes and Measures

The primary end point was the NAR score. Secondary end points included pathologic complete response (pCR) rate, SSS, disease-free survival, and overall survival. This report focuses on end points available after definitive surgery (NAR score, pCR, SSS, clinical complete response rate, margin involvement, and safety).

Results

A total of 185 patients (126 [68.1%] male; mean [SD] age, 55.7 [11.1] years) were randomized to the control arm (CA) (n = 95) or the pembrolizumab arm (PA) (n = 90). Of these patients, 137 were evaluable for NAR score (68 CA patients and 69 PA patients). The mean (SD) NAR score was 11.53 (12.43) for the PA patients (95% CI, 8.54-14.51) vs 14.08 (13.82) for the CA patients (95% CI, 10.74-17.43) (P = .26). The pCR rate was 31.9% in the PA vs 29.4% in the CA (P = .75). The clinical complete response rate was 13.9% in the PA vs 13.6% in the CA (P = .95). The percentage of patients who underwent SSS was 59.4% in the PA vs 71.0% in the CA (P = .15). Grade 3 to 4 adverse events were slightly increased in the PA (48.2%) vs the CA (37.3%) during chemoradiotherapy. Two deaths occurred during FOLFOX: sepsis (CA) and pneumonia (PA). No differences in radiotherapy fractions, FOLFOX, or capecitabine doses were found.

Conclusions and Relevance

Pembrolizumab added to chemoradiotherapy as part of total neoadjuvant therapy was suggested to be safe; however, the NAR score difference does not support further study.

Trial Registration

ClinicalTrials.gov Identifier: NCT02921256.

Abstract 532: Association of pCR and the 8-gene signature: NRG Oncology/NSABP B-41

Background: Lapatinib (L), a HER2 signaling, tyrosine kinase inhibitor, demonstrated numerically higher pCR in NSABP B-41 when added to paclitaxel (AC→P) and trastuzumab (T) following doxorubicin + cyclophosphamide (62% v 52.5%). We previously validated an 8-gene signature that predicted the degree of T benefit in NSABP B-31 and NCCTG9831. The purpose of this study is to determine the association of pCR with the 8- gene T-benefit groups, enabling the possibility of stratifying patients (pts) who do or do not receive benefit from L.

Methods: Normalized B-41 nCounter® Breast Cancer 360 gene expression data was used to define the three T-benefit groups: large-, moderate-, and no-. The 8-gene signature was modified to use only 7 genes because one of the 8 genes was not included in the nCounter code set. The ability of the 7-gene signature to predict T benefit was equivalent to the 8-gene signature when tested in B-31. Comparisons within each treatment arm were made with Fisher's exact test.

Results: The pCR rates were significantly different among the three groups in the AC→P+T arm: Large: 24/28 (86%); Moderate: 13/32 (41%); and No: 1/9 (11%); p&lt;0.001, but were not significantly different in the other two arms; a trend for significance was seen in the AC→P+T+L arm (Table 1). We also tested if L would improve pCR when added to AC→P+T in any of the 7-gene benefit groups compared to T. There was a non-significant, numerical increase in pCR in the no-benefit group in the AC→P+T+L arm (44%) v the AC→P+T arm (11%) (p=0.29).

Conclusions: The significant association of the modified 8-gene benefit groups with pCR in the AC→P+T arm suggests this signature could identify pts who may benefit from dual HER2-targeted neoadjuvant therapy. This could be tested in a meta-analysis including other neoadjuvant trials.

Support: Lombardi CCC; BCRF; GSK; P30CA051008; Genentech; NSABP

Table 1.pCR rates in trastuzumab benefit groups in NSABP B-41pCR rates in Breast and NodesTreatmentNo BenefitIntermediateLarge BenefitEntire Cohortp valueAC→P+T1/9 (11.1%)13/32(40.6%)24/28 (85.7%)38/69 (55.1%)&lt;0.001AC→P+L2/7 (28.6%)11/26 (42.3%)14/31 (45.2%)27/64 (42.2%)0.82AC→P+T+L4/9 (44.4%)11/25 (44.0%)20/27 (74.1%)35/61 (57.4%)0.051

Citation Format: Nan Song, Xiaoqing E. Tan, Ying Wang, Rim S. Kim, Hanna Bandos, Gong Tang, Eleftherios Mamounas, Charles E. Geyer, Priya Rastogi, Samuel A. Jacobs, Ashok Srinivasan, Peter C. Lucas, Soonmyung Paik, Norman Wolmark, Sandra M. Swain, Katherine L. Pogue-Geile. Association of pCR and the 8-gene signature: NRG Oncology/NSABP B-41 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 532.

Examination of the tumor immune microenvironment (TIME) with multispectral immunofluorescence (m-IF): Association of markers with prognosis and bevacizumab (bev) benefit in NRG Oncology/NSABP C-08

3516

Background: The purpose of this study was to quantify different molecules of TIME including T cells, macrophages, and immune checkpoint proteins (ICPs), and determine their association with clinical outcomes and treatment benefit in pts enrolled in C-08, which tested the efficacy of adding bev to 5-fluoruracil+leucovorin+oxaliplatin. Our pre-specified, NCTN-CCSC approved primary objective hypothesized that pts with more CD8 cells would have a better prognosis and receive benefit from bev. Methods: Tissue microarrays were used to assess TIME of 1,509 C-08 pts using m-IF and the Vectra Pathology System. Three m-IF panels were used to quantitatively assess T cells (CD3, CD8, CD45RO, FOXP3), macrophages (CD68, CD163), and ICPs (PD-1, PD-L1, CTLA4, TIM3, LAG3, OX40) in stromal and tumor (panCK) regions. The primary objective was to determine the association between overall survival (OS) and high (top 3rd) v low CD8 expression in both stromal and tumor regions. All markers were tested for associations with OS and recurrence-free interval (RFI) and with bev prediction using Cox models and median cut points. Results: Based on our pre-specified analysis, pts with high CD8 cells had better OS, HR=0.66 (95%CI: 0.49-0.88), p=0.005 but pts with high CD8 cells did not receive bev benefit. All T cells and double stained CD8/PD-1 were associated with better RFI. CD3, CD8, CD68, PD-1, PD-L1, and LAG3 cells were associated with better OS. PD-1 and CD8/PD-1 were associated with RFI in pts with deficient mismatch repair (dMMR) and proficient (p)MMR but TIM3, CD3/CD45RO and CD163 were only associated with RFI in dMMR. Association of CD8 cells with bev benefit (RFI) was seen in dMMR pts, HR 0.27 (95% CI: 0.1-0.73), p=.01 and OS, HR=0.27, (95% CI: 0.12-0.64), p=0.0028 but there was no significant interaction. Single staining CD8, PD-1, and double staining CD8/PD-1 cells were associated with bev benefit in dMMR pts but with bev harm in pMMR pts. However, pts with tumors having >1% of PD-1 and PD-L1 cells (n=197 including 76 dMMR, 100 pMMR, and 21 unknown), received significant bev benefit (int p=.0056). Conclusions: CD8 cells were associated with better OS but were not associated with bev benefit. All T cells and PD-1, PD-L1, and LAG3 cells, were associated with better prognosis in the entire cohort but when pts were stratified for MMR status differences in their association with prognosis and bev benefit emerged. PD-1, CD8, and CD8/PD-1 cells were associated with bev harm in pMMR but bev benefit in dMMR. A significant interaction for the association of high % PD-1 and PD-L1 with bev benefit regardless of MMR status may be a chance finding. However, VEGF has immunosuppressive effects and bev may block these effects in tumors with high PD-L1 and PD-1, regardless of MMR status. NCT: 00096278 PA DOH, U10CA-180868, -180822, -196067, Genentech, Sanofi; NSABP. Clinical trial information: 00096278.

Phase II/III study of Circulating tumOr DNA as a predictive BiomaRker in Adjuvant chemotherapy in patients with stage II colon cancer: NRG-GI005 (COBRA)

TPS3622

Background: There are currently no validated predictive biomarkers for stage II resected colon cancer (CC) after adjuvant chemotherapy. However, circulating tumor DNA (ctDNA) that is shed into the bloodstream represents a highly specific and sensitive approach for identifying microscopic or residual tumor cells. For patients (pts) with CC, the detection of ctDNA is associated with persistent disease after resection and may outperform traditional clinical and pathological features as a prognostic factor to assess risk for recurrence. We hypothesize that for pts whose stage II colon cancer has been resected and who have no traditional high-risk features, a positive ctDNA status may identify those who will benefit from adjuvant chemotherapy. Methods: In this prospective phase II/III clinical trial, pts (N = 1,408) with resected stage II CC without traditional high-risk features and whom the evaluating oncologist deems suitable for no adjuvant chemotherapy will be randomized 1:1 into 2 arms: standard-of-care/observation (Arm A), or prospective testing for ctDNA (Arm B). Postoperative blood will be analyzed for ctDNA with the GuardantHealth LUNAR panel, covering CC-relevant mutations and CC-specific methylation profiling. Pts in Arm B with ctDNA detected will be treated with 6 months of adjuvant (FOLFOX) chemotherapy. For all pts in Arm A, ctDNA status will be analyzed retrospectively at the time of endpoint analysis. The primary endpoints are clearance of ctDNA with adjuvant chemotherapy (phase II) and recurrence-free survival (RFS) for “ctDNA-detected” pts treated with or without adjuvant chemotherapy (phase III). Secondary endpoints will include time-to-event outcomes (OS, RFS, TTR) by ctDNA marker status and treatment, prevalence of detectable ctDNA in stage II CC, and rates of compliance with assigned intervention. Archived normal and matched tumor and blood samples will be collected for exploratory correlative research. The trial is actively accruing towards the phase II endpoint in North America. NCT#: 04068103. Support: U10-CA-180868, -180822; UG1CA-189867; GuardantHealth. Clinical trial information: NCT04068103.

Colorectal Cancer Metastatic dMMR Immuno-Therapy (COMMIT) Study: A randomized phase III study of atezolizumab (atezo) monotherapy versus mFOLFOX6/bevacizumab/atezo in the first-line treatment of patients (pts) with deficient DNA mismatch repair (dMMR) or microsatellite instability high (MSI-H) metastatic colorectal cancer (mCRC)—NRG-GI004/SWOG-S1610

TPS3618

Background: The superiority of inhibition of programmed cell death-1 (PD-1) pathway in dMMR/MSI-H over chemotherapy with either anti-vascular endothelial growth factor receptor (VEGFr) or anti- epithelial growth factor receptor (EGFr) antibodies in mCRC has been demonstrated in a phase III trial (N Engl J Med 2020; 383:2207). However, more patients had progressive disease as the best response in the anti-PD1 monotherapy arm (29.4% vs. 12.3%) with mean progression-free survival (PFS) of 13.7 months. Preclinical models have demonstrated synergistic interactions between FOLFOX, anti-VEGF, and anti-PD-1. We hypothesize that the dMMR/MSI-H mCRC patients may be more effectively treated by the combination of PD-1 pathway blockade and mFOLFOX6/bevacizumab (bev) rather than with anti-PD-L1 therapy (atezo) alone. Methods: Initially a three-arm study, the mFOLFOX6/bev arm was closed to new enrollment on 6-4-20 due to emerging data; the redesigned COMMIT trial was reactivated on 1/29/2021 as a prospective phase III open-label trial that randomizes (1:1) mCRC dMMR/MSI-H pts (N=211) to either atezo monotherapy or mFOLFOX6/bev+atezo combination. Stratification factors include BRAFV600E status, metastatic site, and prior adjuvant CRC therapy. Primary endpoint is PFS as assessed by site investigator. Secondary endpoints include overall survival (OS), objective response rate (RECIST v1.1), safety profile, disease control rate, duration of response, and centrally-reviewed PFS. Health-related quality of life is an exploratory objective. Archived tumor tissue and blood samples will be collected for correlative studies. Key inclusion criteria are: mCRC without prior chemotherapy for advanced disease; dMMR tumor determined by local CLIA-certified IHC assay (MLH1/MSH2/MSH6/PMS2) or MSI-H by local CLIA-certified PCR or NGS panel; and measurable disease per RECIST. Clinical trial: NCT02997228. Support: U10CA180868, -180822, -180888, -180819, UG1CA189867, U24CA196067; Genentech, Inc. Clinical trial information: NCT02997228.

Abstract PS5-01: Biomarkers of resistance to palbociclib in ER+ primary breast cancer in the PALLET trial

Background: CDK4/6 inhibitors are being used in combination with aromatase inhibitors as therapy for advanced ER+ breast cancer (BC) and are being explored for use in primary BC. Few mechanisms driving resistance to added CDK4/6 inhibitors have been defined. The PALLET phase II randomized neoadjuvant trial of letrozole (LET) ± palbociclib (PALBO) in postmenopausal ER+HER2- primary BC reported that clinical response rate over 14wks was not significantly increased by adding PALBO to LET but suppression of Ki67 was significantly increased (Johnston et al, JCO 2018, 37, 178): after 14wks complete cell cycle arrest (CCCA, Ki67&lt;2.7%) was present in 59% on LET and 90% on LET+PALBO. Here we sought to identify biomarkers of de novo resistance to allow selection of patients most likely to benefit from added PALBO.

Methods: 307 patients were randomized to LET (n=103) or LET+PALBO (n=204) for 14 wks. The first 2wks of LET+PALBO patients were randomised to LET, PALBO, or LET+PALBO. Biopsies were taken at baseline, 2wks and 14wks. Biomarker data are presented here for baseline only, other than Ki67 at both baseline and 14wks. IHC analyses were conducted on FFPE biopsies for ER, PgR, RB1, cyclin-E1, and cyclin-D1 (also FISH). RNA-seq was performed on fresh frozen biopsies. Association of each biomarker with CCCA was determined by logistic regression. Differentially expressed genes (DEGs) were identified between patients sensitive (CCCA) (n=94) and resistant (non-CCCA) (n=10) to treatments with or without PALBO at 14wks by DESeq2. Fifty hallmark gene sets were tested for significant enrichment with DEGs and differential gene sets were identified by using Gene Set Enrichment Analysis (GSEA).

Results: The association of IHC biomarkers with CCCA is shown in the table. Lower levels of ER, higher levels of cyclin-E1, and amplification of cyclin-D1 were each significantly associated with a greater chance of non-CCCA with LET+PALBO. High cyclin-E1 levels were also associated with reduced chance of CCCA with LET only. Patients with high baseline Ki67 also exhibited higher non-CCCA with LET+PALBO at 14wks (p=0.0002). In the RNAseq data we identified 1973 DEGs between the 14wk CCCA and non-CCCA patients for LET+PALBO. E2F and MYC targets, PI3K/AKT/MTOR signalling and interferon response gene sets were among the hallmark gene sets enriched for genes with higher expression in non-CCCA patients at 14wks for LET+PALBO (FDR&lt;0.05). For LET-only, 311 DEGs were identified and the “Estrogen Response Early” gene set was significantly enriched in genes with higher expression in CCCA samples. At the individual gene level, genes significantly associated with non-CCCA after 14wks LET+PALBO included CCNE1, CDK2 and several E2F-related genes (p&lt;0.05). Their expression was not significantly different between non-CCCA and CCCA patients with LET alone.

Conclusion: Biomarkers associated with response/resistance to added PALBO were different from LET only. PALBO resistance was associated with higher baseline expression of cyclin-E1 (both IHC and RNA), CDK2, and genes related to E2F, MYC, interferon and MTOR signalling. These results suggest that multiple identifiable mechanisms of de novo resistance to PALBO are likely to exist in primary ER+ BC. On-going WES analyses will allow the significance of alterations at the DNA level to be presented.

Table 1.Continuous measurement in a logistic regression for CCCA at 14 weeks; Oddsratio calculated separately for group A and groups B,C,D and were adjusted forregion (UK vs NA); * amplified vsnon-amplifiedContinuous measurement in a logistic regression for CCCA at 14 weeksBiomarkerLET LET+PALBOOdds ratio95% CIpOdds ratio95% CIpER1.120.36, 3.480.844.471.62, 12.380.004PgR4.381.03, 18.580.053.050.50, 18.560.23RB13.010.24, 38.560.400.420.05, 38.490.83Cyclin-E10.100.01, 0.840.030.020.00, 0.200.001Cyclin-D1 IHC3.090.51, 18.490.222.560.28, 23.330.40CyclinD1 FISH*1.470.43, 4.990.530.280.06, 0.860.03

Citation Format: Eugene F Schuster, Hui Xiao, Elena Lopez-Knowles, Lucy Kilburn, Mothaffar Rimawi, David A Wheeler, Katherine Pogue-Geile, Yuan Lui, Samuel A Jacobs, Chet Cornman, Shannon Puhalla, Maggie Cheang, Judith Bliss, Stephen Johnston, Mitch Dowsett, On behalf of the PALLET Trialists. Biomarkers of resistance to palbociclib in ER+ primary breast cancer in the PALLET trial [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS5-01.

NRG-GI004/SWOG-S1610: Colorectal Cancer Metastatic dMMR Immuno-Therapy (COMMIT) Study—A randomized phase III study of atezolizumab (atezo) monotherapy versus mFOLFOX6/bevacizumab/atezo in the first-line treatment of patients (pts) with deficient DNA mismatch repair (dMMR) or microsatellite instability high (MSI-H) metastatic colorectal cancer (mCRC)

TPS158

Background: Despite activity of programmed cell death-1 (PD-1) pathway inhibition in dMMR/MSI-H mCRC, approximately one-third of patients demonstrate progressive disease as best response to anti-PD1 monotherapy. Preclinical models have demonstrated synergistic interactions between FOLFOX, anti-VEGF, and anti-PD-1. We hypothesize that the dMMR/MSI-H mCRC subset may be more effectively targeted by the combination of PD-1 pathway blockade and mFOLFOX6/bevacizumab (bev) rather than with anti-PD-1 therapy (atezo) alone. Methods: Initially a three-arm study, the mFOLFOX6/bev arm was closed to new enrollment on 6-4-20 due to emerging data; the redesigned COMMIT is a prospective phase III open-label trial that will randomize (1:1) mCRC dMMR/MSI-H pts (N=211) to either atezo monotherapy or mFOLFOX6/bev+atezo combination. Stratification factors include BRAFV600E status, metastatic site, and prior adjuvant CRC therapy. Primary endpoint is progression-free survival (PFS) as assessed by site investigator. Secondary endpoints include OS, objective response rate, safety profile, disease control rate, duration of response, and centrally-reviewed PFS. Health-related quality of life is an exploratory objective. Archived tumor tissue and blood samples will be collected for correlative studies. Key inclusion criteria are: mCRC without prior chemotherapy for advanced disease; dMMR tumor determined by local CLIA-certified IHC assay (MLH1/MSH2/MSH6/PMS2) or MSI-H by local CLIA-certified PCR or NGS panel; and measurable disease per RECIST. Support: U10CA180868, -180822, -180888, -180819, UG1CA189867, U24CA196067; Genentech, Inc. Clinical trial information: NCT02997228.

NRG-GI002: A phase II clinical trial platform using total neoadjuvant therapy (TNT) in locally advanced rectal cancer (LARC)—Pembrolizumab experimental arm (EA) primary results

8

Background: This NCTN multi-arm randomized phase II modular clinical trial platform utilizes TNT with parallel EAs in LARC. EAs are not intended for direct comparison, but rather to test a variety of sensitizers or hypotheses in a consistent and homogenous high-risk pt population with correlative biomarkers. Here we report the primary and available secondary endpoints (EPs). Methods: Stage II/III LARC pts (with ONE or more of the following: distal location [cT3-4 ≤5cm from anal verge, any N]; bulky [any cT4 or tumor within 3mm of mesorectal fascia]; high risk for metastatic disease [cN2]; or not a sphincter-sparing surgery [SSS] candidate) were randomized to neoadjuvant FOLFOX x 4mo → chemoRT (capecitabine with 50.4Gy +/- pembrolizumab 200mg IV Q3 wks x 6 doses) → surgery 8-12 wks following last dose of radiotherapy. Primary EP: Improvement in Neoadjuvant Rectal Cancer (NAR) score for EA v control potentially representing a 3-4% absolute OS improvement. Secondary EPs: Comparisons of OS, DFS, toxicity, pCR, cCR, therapy completion, negative surgical margins, sphincter sparing surgery (SSS), and exploratory assessments of molecular and radiographic predictors of response and distant failure. Binary EPs compared by Fisher’s exact test. Reported p-values are two-sided. Results: From 8/2018-5/2019, 185 pts were randomized to control (n=95) or pembrolizumab (n= 90). Baseline characteristics were relatively well balanced. 137 pts were evaluable for NAR (68 control, 69 pembrolizumab). Mean NAR was 14.08 for control (95% CI: 10.7-17.4) v 11.53 for pembrolizumab (CI: 8.5-14.6) (p=0.26). pCR=29.4% v 31.9% (p=0.75); cCR=13.6% v 13.9% (p=0.95); and SSS=71.0% v 59.4% (p=0.15). The side effects on Arm 3 were consistent with both CRT and pembrolizumab safety profile. Grade 3/4 AEs were slightly increased on the pembrolizumab arm during and after CRT (48.2 v 37.3%). There were 2 deaths during FOLFOX, one on the control arm due to sepsis; the other on the EA due to pneumonia. There were no statistically significant differences in RT (fractions, dose, boost fractions, or boost dose), FOLFOX or capecitabine doses. Conclusions: Pembrolizumab added to chemoRT as part of TNT was safe and without unexpected short-term toxicities but failed to improve the NAR score. The secondary endpoints including PFS and OS have not been reached. Correlative analysis for both T-cell and myeloid cell populations in the tissue and blood in addition to comprehensive cytokine analysis is ongoing. NCT02921256. Support: U10CA180868, -180822; UG1-189867; U24-196067. Clinical trial information: NCT02921256.

Phase II/III study of circulating tumor DNA as a predictive biomarker in adjuvant chemotherapy in patients with stage II colon cancer:NRG-GI005 (COBRA)

TPS148

Background: There are currently no validated predictive biomarkers for stage II resected colon cancer (CC) after adjuvant chemotherapy. However, circulating tumor DNA (ctDNA) that is shed into the bloodstream represents a highly specific and sensitive approach for identifying microscopic or residual tumor cells. For patients (pts) with CC, the detection of ctDNA is associated with persistent disease after resection and may outperform traditional clinical and pathological features as a prognostic factor to assess risk for recurrence. We hypothesize that for pts whose stage II colon cancer has been resected and who have no traditional high-risk features, a positive ctDNA status may identify those who will benefit from adjuvant chemotherapy. Methods: In this prospective phase II/III clinical trial, pts (N=1,408) with resected stage II CC without traditional high-risk features and whom the evaluating oncologist deems suitable for no adjuvant chemotherapy will be randomized 1:1 into 2 arms:standard-of-care/observation (Arm A), or prospective testing for ctDNA (Arm B). Postoperative blood will be analyzed for ctDNA with the GuardantHealth LUNAR panel, covering CC-relevant mutations and CC-specific methylation profiling. Pts in Arm B with ctDNA detected will be treated with 6 months of adjuvant (FOLFOX) chemotherapy. For all pts in Arm A, ctDNA status will be analyzed retrospectively at the time of endpoint analysis. The primary endpoints are clearance of ctDNA with adjuvant chemotherapy (phase II) and recurrence-free survival (RFS) for “ctDNA-detected” pts treated with or without adjuvant chemotherapy (phase III). Secondary endpoints will include time-to-event outcomes (OS, RFS, TTR) by ctDNA marker status and treatment, prevalence of detectable ctDNA in stage II CC, and rates of compliance with assigned intervention. Archived normal and matched tumor and blood samples will be collected for exploratory correlative research. The trial is actively accruing towards the phase II endpoint across all US and Canadian cooperative groups. Support:U10-CA-180868, -180822; UG1CA-189867; GuardantHealth. Clinical trial information: NCT04068103.

ctDNA applications and integration in colorectal cancer: an NCI Colon and Rectal-Anal Task Forces whitepaper

An increasing number of studies are describing potential uses of circulating tumour DNA (ctDNA) in the care of patients with colorectal cancer. Owing to this rapidly developing area of research, the Colon and Rectal-Anal Task Forces of the United States National Cancer Institute convened a panel of multidisciplinary experts to summarize current data on the utility of ctDNA in the management of colorectal cancer and to provide guidance in promoting the efficient development and integration of this technology into clinical care. The panel focused on four key areas in which ctDNA has the potential to change clinical practice, including the detection of minimal residual disease, the management of patients with rectal cancer, monitoring responses to therapy, and tracking clonal dynamics in response to targeted therapies and other systemic treatments. The panel also provides general guidelines with relevance for ctDNA-related research efforts, irrespective of indication.

Neratinib-Plus-Cetuximab in Quadruple-WT (KRAS, NRAS, BRAF, PIK3CA) Metastatic Colorectal Cancer Resistant to Cetuximab or Panitumumab: NSABP FC-7, A Phase Ib Study

PURPOSE

In metastatic colorectal cancer (mCRC), HER2 (ERBB2) gene amplification is implicated in anti-EGFR therapy resistance. We sought to determine the recommended phase II dose (RP2D) and efficacy of neratinib, a pan-ERBB kinase inhibitor, combined with cetuximab, in patients with progressive disease (PD) on anti-EGFR treatment.

PATIENTS AND METHODS

Twenty-one patients with quadruple-wild-type, refractory mCRC enrolled in this 3+3 phase Ib study. Standard dosage cetuximab was administered with neratinib at 120 mg, 160 mg, 200 mg, and 240 mg/day orally in 28-day cycles. Samples were collected for molecular and pharmacokinetic studies.

RESULTS

Sixteen patients were evaluable for dose-limiting toxicity (DLT). 240 mg was determined to be the RP2D wherein a single DLT occurred (1/7 patients). Treatment-related DLTs were not seen at lower doses. Best response was stable disease (SD) in 7 of 16 (44%) patients. HER2 amplification (chromogenic in situ IHC) was detected in 2 of 21 (9.5%) treatment-naïve tumors and 4 of 16 (25%) biopsies upon trial enrollment (post-anti-EGFR treatment and progression). Compared with matched enrollment biopsies, 6 of 8 (75%) blood samples showed concordance for HER2 CNV in circulating cell-free DNA. Five SD patients had HER2 amplification in either treatment-naïve or enrollment biopsies. Examination of gene-expression, total protein, and protein phosphorylation levels showed relative upregulation of ≥2 members of the HER-family receptors or ligands upon enrollment versus matched treatment-naïve samples.

CONCLUSIONS

The RP2D of neratinib in this combination was 240 mg/day, which was well tolerated with low incidence of G3 AEs. There were no objective responses; SD was seen at all neratinib doses. HER2 amplification, detectable in both tissue and blood, was more frequent post-anti-EGFR therapy.

Evidence-based guidelines for managing patients with primary ER+ HER2- breast cancer deferred from surgery due to the COVID-19 pandemic

Many patients with ER+ HER2- primary breast cancer are being deferred from surgery to neoadjuvant endocrine therapy (NeoET) during the COVID-19 pandemic. We have collated data from multiple international trials of presurgical endocrine therapy in order to provide guidance on the identification of patients who may have insufficiently endocrine-sensitive tumors and should be prioritised for early surgery or neoadjuvant chemotherapy rather than NeoET during or in the aftermath of the COVID-19 pandemic for safety or when surgical activity needs to be prioritized. For postmenopausal patients, our data provide strong support for the use of ER and PgR status at diagnosis for triaging of patients into three groups in which (taking into account clinical factors): (i) NeoET is likely to be inappropriate (Allred ER <6 or ER 6 and PgR <6) (ii) a biopsy for Ki67 analysis (on-treatment Ki67) could be considered after 2-4 weeks of NeoET (a: ER 7 or 8 and PgR <6 or b: ER 6 or 7 and PgR ≥6) or (iii) NeoET is an acceptable course of action (ER 8 and PgR ≥6). Cut-offs for percentage of cells positive are also given. For group (ii), a high early on-treatment level of Ki67 (>10%) indicates a higher priority for early surgery. Too few data were available for premenopausal patients to provide a similar treatment algorithm. These guidelines should be helpful for managing patients with early ER+ HER2- breast cancer during and in the aftermath of the COVID-19 crisis.

Phase II/III study of circulating tumor DNA as a predictive biomarker in adjuvant chemotherapy in patients with stage II colon cancer: NRG-GI005 (COBRA)

TPS4121

Background: There are currently no validated predictive biomarkers for stage II resected colon cancer (CC) after adjuvant chemotherapy. However, circulating tumor DNA (ctDNA) that is shed into the bloodstream represents a highly specific and sensitive approach for identifying microscopic or residual tumor cells. For patients (pts) with CC, the detection of ctDNA is associated with persistent disease after resection and may outperform traditional clinical and pathological features as a prognostic factor to assess risk for recurrence. We hypothesize that for pts whose stage II colon cancer has been resected and who have no traditional high-risk features, a positive ctDNA status may identify those who will benefit from adjuvant chemotherapy. Methods: In this prospective phase II/III clinical trial, pts (N=1,408) with resected stage II CC without traditional high-risk features and whom the evaluating oncologist deems suitable for no adjuvant chemotherapy will be randomized 1:1 into 2 arms: standard-of-care/observation (Arm A), or prospective testing for ctDNA (Arm B). Postoperative blood will be analyzed for ctDNA with the GuardantHealth LUNAR panel, covering CC-relevant mutations and CC-specific methylation profiling. Pts in Arm B with ctDNA detected will be treated with 6 months of adjuvant (FOLFOX) chemotherapy. For all pts in Arm A, ctDNA status will be analyzed retrospectively at the time of endpoint analysis. The primary endpoints are clearance of ctDNA with adjuvant chemotherapy (phase II) and recurrence-free survival (RFS) for “ctDNA-detected” pts treated with or without adjuvant chemotherapy (phase III). Secondary endpoints will include time-to-event outcomes (OS, RFS, TTR) by ctDNA marker status and treatment, prevalence of detectable ctDNA in stage II CC, and rates of compliance with assigned intervention. Archived normal and matched tumor and blood samples will be collected for exploratory correlative research. The trial is actively accruing towards the phase II endpoint across all US and Canadian cooperative groups. Support: U10-CA-180868, -180822; UG1CA-189867; GuardantHealth. Clinical trial information: NCT04068103 .

Abstract OT2-02-03: NSABP FB-13: An assessment of the biological and clinical effects of palbociclib with ovarian suppression and letrozole in the neoadjuvant treatment of pts (pts) with premenopausal (preM) estrogen-receptor positive/HER2-negative primary breast cancer

Background: There have been few studies of neoadjuvant endocrine therapy in premenopausal (preM) women despite low pathologic complete response (pCR) rates using neoadjuvant chemotherapy in ER+/HER2− pts. Suppression of Ki67, particularly complete cell cycle arrest (CCCA) defined as Ki67 &lt;2.7% after 2 wks of neoadjuvant endocrine therapy has been demonstrated to correlate with recurrence-free survival. PALLET, a randomized, neoadjuvant endocrine trial evaluated letrozole (AI) v palbociclib (pal) in combination with AI for 14 wks in post-menopausal women. This study demonstrated a modest improvement in clinical response (54.3% with the combination v 49.5% with AI alone) but showed a significant difference in achievement of CCCA (Ki67&lt;2.7%) with the combination of pal and AI v AI alone (90% v 59%). We seek to evaluate this combination, given over a longer duration in the neoadjuvant setting, in preM women with early-stage breast cancer. Trial design: FB-13 is a phase II, open-label study to examine the biological and clinical effect of neoadjuvant endocrine therapy with AI, pal, and ovarian suppression in preM pts with ER+, HER2-negative early invasive breast cancer. 76 pts will be stratified into one of two approximately equal sized cohorts based on Oncotype DX Breast Recurrence Score (RS) (cohort 1: pts with RS &lt;11 or cohort 2: pts with RS 11 to &lt;26). A baseline tumor biopsy prior to start of therapy (tx) for RS and Ki67 will both be centrally determined. Pts in both cohorts will receive letrozole 2.5 mg by mouth daily, pal 125 mg by mouth daily for 21 days of a 28-day cycle, and goserelin 3.6 mg SQ injection every 28 days. At wk 6, pts will have core-cut biopsies for real-time evaluation of Ki67. Pts from both cohorts who have Ki67 &lt;10% will continue tx for a total of 6 cycles. Pts with a persistent Ki67 ≥10% will permanently discontinue tx and begin neoadjuvant chemotherapy or proceed to surgery at physician discretion. Eligibility: FB-13 is enrolling preM women newly diagnosed with ER+/HER2− early breast cancer who are candidates for neoadjuvant endocrine therapy. Pts must be preM based on standard definitions. Primary tumor size must be &gt;2 cm. RS must be &lt;26. Mandatory pre-treatment and post-surgical samples will be collected and analyzed for RS and Ki67, as well as additional biomarkers to correlate with response. Blood will be collected at baseline, 4 wks, and at 24 wks for estradiol levels to demonstrate ovarian suppression. A 4-wk estradiol level in the postmenopausal range will be required to receive further treatment. Specific aims: The primary aim is to determine complete cell cycle arrest as indicated by a Ki67 &lt;2.7% at 6 wks. Secondary aims are to determine overall response rate (ORR) by clinical exam and ultrasound, the pCR, to generate a Preoperative Endocrine Prognostic Index (PEPI score), to compare the change in Ki67 at baseline, after 6 wks and 24 wks, and to determine the rate of breast-conservation therapy. Statistical methods: We anticipate that the addition of palbociclib to ovarian suppression and AI will result in a measurable drop in Ki67 and a high ORR. The null hypothesis is ORR &lt;40% and alternative hypothesis is ORR &gt;60%. We anticipate that &gt;60% of pts in each cohort will have 6 wk Ki67 &lt;2.7% and clinical response &gt;35%. Present accrual and target accrual: Currently 12 of a planned 76 pts have been enrolled. NSABP Operations contact information: Diana Gosik, Diana.Gosik@nsabp.org NCT03628066 SUPPORT: Genomic Health Inc, Pfizer, NSABP Foundation

Citation Format: Shannon Puhalla, Greg Yothers, Amy P Sing, Thomas B Julian, Norman Wolmark, Samuel A Jacobs. NSABP FB-13: An assessment of the biological and clinical effects of palbociclib with ovarian suppression and letrozole in the neoadjuvant treatment of pts (pts) with premenopausal (preM) estrogen-receptor positive/HER2-negative primary breast cancer [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr OT2-02-03.

A randomized phase III study of mFOLFOX6/bevacizumab combination chemotherapy with or without atezolizumab or atezolizumab monotherapy in the first-line treatment of patients (pts) with deficient DNA mismatch repair (dMMR) metastatic colorectal cancer (mCRC): Colorectal Cancer Metastatic dMMR Immuno-Therapy (COMMIT) study (NRG-GI004/SWOG-S1610)

TPS260

Background: Deficient DNA mismatch repair (dMMR) colorectal cancer (CRC) is highly immunogenic. Preclinical data showed synergistic interactions among FOLFOX, anti-VEGF, and programmed cell death-1 (PD-1) pathway blockade. Prior phase I study of mFOLFOX6/ bevacizumab (bev) + atezolizumab (atezo) was well tolerated and enhanced intratumoral infiltration of CD8+ T cells. We hypothesize that the dMMR subset of CRC may be effectively targeted with combination of PD-1 pathway blockade and mFOLFOX6/bev. Methods: This is a prospective randomized phase III open-label trial. Pts (N=347) with mCRC dMMR will be randomized to three trial arms (1:1:1): mFOLFOX6/bev; atezo monotherapy; or mFOLFOX6/bev + atezo. Stratification factors include BRAFV600E status, metastatic site, and prior adjuvant CRC therapy. Primary endpoint is progression-free survival (PFS) assessed by study investigator of mFOLFOX6/bev/atezo and atezo monotherapy compared to mFOLFOX6/bev. Secondary endpoints include OS, objective response rate, safety profile, disease control rate, duration of response, and PFS by retrospective central review. Health-related quality of life is an exploratory objective. Archived tumor tissue and blood samples will be collected for correlative studies. Key inclusion criteria are: mCRC without prior chemotherapy for advanced disease; dMMR tumor determined by local CLIA-certified IHC assay (MLH1/MSH2/MSH6/PMS2); availability of archived tumor tissue for central confirmation of dMMR status; and measurable disease per RECIST. Activated 11-7-17. As of 9-11-19, enrollment continues with 44/347 pts enrolled. Clinical trial: NCT02997228. Support:U10CA180868, -180822, -180888, -180819, UG1CA189867, U24CA196067; Genentech, Inc. Clinical trial information: NCT02997228.

NRG-GI005 (COBRA): Phase II/III study of circulating tumor DNA as a predictive biomarker in adjuvant chemotherapy in patients with stage II colon cancer

TPS261

Background: There are currently no validated predictive biomarkers for stage II resected colon cancer (CC) after adjuvant chemotherapy. However, circulating tumor DNA (ctDNA) that is shed into the bloodstream represents a highly specific and sensitive approach for identifying microscopic or residual tumor cells. For patients (pts) with CC, the detection of ctDNA is associated with persistent disease after resection and may outperform traditional clinical and pathological features as a prognostic factor to assess risk for recurrence. We hypothesize that for pts whose stage II colon cancer has been resected and who have no traditional high-risk features, a positive ctDNA status may identify those who will benefit from adjuvant chemotherapy. Methods: In this prospective phase II/III clinical trial, pts (N=1,408) with resected stage II CC without traditional high-risk features and whom the evaluating oncologist deems suitable for no adjuvant chemotherapy will be randomized 1:1 into 2 arms: standard-of-care/observation (Arm A), or prospective testing for ctDNA (Arm B). Postoperative blood will be analyzed for ctDNA with the GuardantHealth LUNAR panel, covering CC-relevant mutations and CC-specific methylation profiling. Pts in Arm B with ctDNA detected will be treated with 6 months of adjuvant (FOLFOX) chemotherapy. For all pts in Arm A, ctDNA status will be analyzed retrospectively at the time of endpoint analysis. The primary endpoints are clearance of ctDNA with adjuvant chemotherapy (phase II) and recurrence-free survival (RFS) for “ctDNA-detected” pts treated with or without adjuvant chemotherapy (phase III). Secondary endpoints will include time-to-event outcomes (OS, RFS, TTR) by ctDNA marker status and treatment, prevalence of detectable ctDNA in stage II CC, and rates of compliance with assigned intervention. Archived normal and matched tumor and blood samples will be collected for exploratory correlative research. Trial accrual is anticipated across all US and Canadian cooperative groups.NCT#: 04068103. Support: U10-CA-180868, -180822; UG1CA-189867; GuardantHealth. Clinical trial information: 04068103.

NSABP FR-2: Phase II study of durvalumab following neoadjuvant chemoRT in stage II-IV rectal cancer

TPS264

Background: Clinical improvements for locally advanced rectal cancer have been relatively static over the past few decades. While immunotherapy shows no benefit in microsatellite stable (MSS) colorectal cancer, preclinical models suggest that radiotherapy (RT) can enhance neoantigen presentation, modulate the microenvironment, and improve the likelihood of anti-tumor activity with checkpoint inhibitor use. Using a “window-of-opportunity” study design, this prospective phase II trial will determine the safety and activity of this approach with the anti-PD-L1 agent durvalumab (MEDI4736). Methods: This multi-center phase II trial is currently enrolling patients (pts) with rectal cancer who are undergoing standard NCCN guideline-compliant neoadjuvant chemoradiotherapy (CRT). Eligibility includes pts with MSS stage II-IV rectal cancer with adequate organ function and pre-treatment diagnostic tumor available for profiling with intent to proceed to surgical resection after CRT. Stage IV disease must be limited such that the primary pelvic tumor requires definitive management. Standard ineligibility criteria include active infections, systemic steroid use, or other conditions making immunotherapy use unsafe. Treatment includes durvalumab (750mg IV infusion once every 2 wks) for 4 total doses beginning within 3-7 days after CRT completion. Surgery must be within 8-12 wks of the final CRT dose. Primary endpoint is a demonstrated improvement in Neoadjuvant Rectal Cancer (NAR) score compared to historical controls targeting a 20% relative risk reduction in DFS and 3-4% absolute OS improvement. Secondary endpoints include OS, DFS, toxicity, pCR, cCR, therapy completion, negative surgical margins, sphincter preservation, off-target “abscopal” effects for the subset of stage IV pts, and exploratory assessments of tumor infiltrating lymphocytes, tumor Immunoscore, circulating immunologic profiles, and molecular predictors of response. A safety run-in phase has completed as a precedent to full enrollment. Enrollment now continues to 47 total pts to achieve 41 surgically evaluable pts. Support: AstraZeneca-Medimmune, NSABP Foundation. Clinical trial information: NCT03102047.

NSABP FC-10: Phase IB study of pembrolizumab in combination with premetrexed + oaliplatin in patients (pts) with chemo-refractory metastatic colorectal cancer (mCRC)

TPS262

Background: The majority of mCRC pts are microsatellite stable (MSS), have poor intratumoral CD8+ T cell infiltration, and no clinical response to immunotherapy checkpoint inhibitors. Preclinical studies suggest that chemotherapy may synergize with anti-PD-1. In non-small cell lung cancer (NSCLC), the combination of pembrolizumab (PemB), pemetrexed (PemT), + carboplatin demonstrated synergistic activity. This study will combine PemB with PemT, then that combination + oxaliplatin (Ox). The rationale for addition of Ox to PemT is that enhanced immunogenic cell death may induce CD8+ T cell infiltration into CRC tumors and model the mechanism of cytotoxicity seen in NSCLC. Thus, the combination of PemB+ PemT + Ox may induce synergistic antitumor immune activity. Methods: This multi-center phase Ib trial is actively enrolling pts with incurable mCRC with prior treatment for mCRC including fluoropyrimidine-, oxaliplatin-, and irinotecan-based chemotherapy, and if RAS wild-type, anti-EGFR therapy. Measurable disease by imaging (RECIST 1.1) is required. Standard ineligibility includes active infections, systemic steroid use, or other conditions contraindicating immunotherapy. Cohort 1 will receive PemB + PemT; Cohort 2 will receive PemB + PemT + dose-escalated Ox. Imaging will be performed every 6 wks. The primary aim of Cohort 1: to evaluate for safety and efficacy using doses of PemB and PemT that have been studied in NSCLC. The primary aim of Cohort 2: to evaluate the safety, tolerability, and efficacy of PemB in combination with PemT + Ox. The RP2D of the 3-drug combination will be at the MTD taking into account toxicity profiles of study therapy agents. Secondary aims: to evaluate the clinical benefit rate of the doublet and triplet combinations in pts with chemo-refractory MSS mCRC and to estimate progression-free survival and overall survival in pts with MSS mCRC treated with these combinations. The cohorts will be analyzed separately with descriptive intent only. Maximum enrollment is 33 pts. Support: Merck; Lilly; NSABP Foundation, Inc. Clinical trial information: NCT03626922.

NSABP FB-7: a phase II randomized neoadjuvant trial with paclitaxel + trastuzumab and/or neratinib followed by chemotherapy and postoperative trastuzumab in HER2+ breast cancer

PURPOSE

The primary aim of NSABP FB-7 was to determine the pathologic complete response (pCR) rate in locally advanced HER2-positive (HER2⁺) breast cancer patients treated with neoadjuvant trastuzumab or neratinib or the combination and weekly paclitaxel followed by standard doxorubicin plus cyclophosphamide. The secondary aims include biomarker analyses.

EXPERIMENTAL DESIGN

pCR was tested for association with treatment, gene expression, and a single nucleotide polymorphism (SNP) in the Fc fragment of the IgG receptor IIIa-158V/F (FCGR3A). Pre-treatment biopsies and residual tumors were also compared to identify molecular changes.

RESULTS

The numerical pCR rate in the trastuzumab plus neratinib arm (50% [95%CI 34-66%]) was greater than that for single-targeted therapies with trastuzumab (38% [95%CI 24-54]) or neratinib (33% [95%CI 20-50]) in the overall cohort but was not statistically significant. Hormone receptor-negative (HR^-) tumors had a higher pCR rate than HR⁺ tumors in all three treatment arms, with the highest pCR rate in the combination arm. Diarrhea was the most frequent adverse event and occurred in virtually all patients who received neratinib-based therapy. Grade 3 diarrhea was reported in 31% of patients; there were no grade 4 events. Our 8-gene signature, previously validated for trastuzumab benefit in two different clinical trials in the adjuvant setting, was correlated with pCR across all arms of NSABP FB-7. Specifically, patients predicted to receive no trastuzumab benefit had a significantly lower pCR rate than did patients predicted to receive the most benefit (P = 0.03). FCGR genotyping showed that patients who were homozygous for the Fc low-binding phenylalanine (F) allele for FCGR3A-158V/F were less likely to achieve pCR.

CONCLUSIONS

Combining trastuzumab plus neratinib with paclitaxel increased the absolute pCR rate in the overall cohort and in HR^- patients. The 8-gene signature, which is validated for predicting trastuzumab benefit in the adjuvant setting, was associated with pCR in the neoadjuvant setting, but remains to be validated as a predictive marker in a larger neoadjuvant clinical trial. HR status, and the FCGR3A-158V/F genotype, also warrant further investigation to identify HER2⁺ patients who may benefit from additional anti-HER2 therapies beyond trastuzumab. All of these markers will require further validation in the neoadjuvant setting.

TRIALS REGISTRATION

ClinicalTrials.gov, NCT01008150. Retrospectively registered on October 5, 2010.

Safety and Efficacy of T-DM1 Plus Neratinib in Patients With Metastatic HER2-Positive Breast Cancer: NSABP Foundation Trial FB-10

PURPOSE

Patients with human epidermal growth factor receptor 2 (HER2)–positive metastatic breast cancer eventually develop resistance to dual-antibody therapy with trastuzumab plus pertuzumab. Mechanisms of resistance have not been well elucidated. We evaluated the safety, tolerability, and efficacy of ado-trastuzumab emtansine (T-DM1) plus neratinib in patients who progressed on trastuzumab plus pertuzumab.

PATIENTS AND METHODS

In this 3 + 3 dose-escalation study, patients with metastatic breast cancer who progressed on trastuzumab, pertuzumab, and a taxane were treated with T-DM1 at 3.6 mg/kg intravenously every 3 weeks and dose-escalating neratinib at 120, 160, 200, or 240 mg/d orally.

RESULTS

Twenty-seven patients were treated across four dose-levels of neratinib. Dose-limiting toxicity in cycle 1 was grade 3 diarrhea in six patients and grade 3 nausea in one; no patient experienced grade 4 diarrhea, and there were no grade 5 toxicities. Other grade 3 to 4 toxicities included nausea (11%), dehydration (11%), electrolyte abnormality (19%), thrombocytopenia (15%), elevated transaminase levels (7%), and fatigue (7%). Twelve (63%) of 19 evaluable patients had an objective response. Responses occurred at all neratinib doses. Plasma cell–free DNA at baseline showed ERBB2 (HER2) amplification in 10 of 27 patients. Deep and more durable responses occurred in patients with cell-free DNA ERBB2 amplification. Two complete responders had high expression of total HER2 and p95HER2 in baseline tissue.

CONCLUSION

We report the recommended phase II dose of T-DM1 3.6 mg/kg and neratinib 160 mg/d for this combination. Possible resistance mechanisms to HER2 antibodies may be loss of the HER2 receptor and high expression of p95HER2. These data provide the basis for an ongoing phase II study to better define the activity of this regimen.

National Cancer Institute (NCI) state of the science: Targeted radiosensitizers in colorectal cancer

Colorectal cancer (CRC) represents a major public health problem as the second leading cause of cancer-related mortality in the United States. Of an estimated 140,000 newly diagnosed CRC cases in 2018, roughly one-third of these patients will have a primary tumor located in the distal large bowel or rectum. The current standard-of-care approach includes curative-intent surgery, often after preoperative (neoadjuvant) radiotherapy (RT), to increase rates of tumor down-staging, clinical and pathologic response, as well as improving surgical resection quality. However, despite advancements in surgical techniques, as well as sharpened precision of dosimetry offered by contemporary RT delivery platforms, the oncology community continues to face challenges related to disease relapse. Ongoing investigations are aimed at testing novel radiosensitizing agents and treatments that might exploit the systemic antitumor effects of RT using immunotherapies. If successful, these treatments may usher in a new curative paradigm for rectal cancers, such that surgical interventions may be avoided. Importantly, this disease offers an opportunity to correlate matched paired biopsies, radiographic response, and molecular mechanisms of treatment sensitivity and resistance with clinical outcomes. Herein, the authors highlight the available evidence from preclinical models and early-phase studies, with an emphasis on promising developmental therapeutics undergoing prospective validation in larger scale clinical trials. This review by the National Cancer Institute's Radiation Research Program Colorectal Cancer Working Group provides an updated, comprehensive examination of the continuously evolving state of the science regarding radiosensitizer drug development in the curative treatment of CRC.

Abstract 4064: Association of molecular signatures, mutations, and sTILs, with pCR in breast cancer patients in NRG Oncology/NSABP B-52

Background: NRG Oncology/NSABP B-52 neoadjuvant clinical trial was conducted to test if the addition of estrogen deprivation (ED) would improve the pCR rate in HER2+/ER+ breast cancer pts treated with docetaxel, carboplatin, trastuzumab, and pertuzumab (TCHP). A numerical increase in the pCR rate was observed with ED (46.1% v 40.9%), but the difference was not statistically significant. The purpose of this study was to determine the utility of using stromal tumor infiltrating lymphocytes (sTILs), mutations, established, and novel signatures, to assess their value for predicting pCR, particularly in the TCHP + ED arm.

Methods: Whole transcriptome RNA-Seq and Ampli-Seq libraries were sequenced on the Ion Torrent platform. Mutations were assessed with a custom Ampli-Seq panel of 117 genes, including HER2-activated pathways and/or trastuzumab (T)-resistance markers. The 8-gene T-benefit signature was prospectively tested for association with pCR, and was previously validated in the adjuvant setting in B-31 and NCCTG N9831. Hot-spot mutations, sTILs, and signatures for immune cells, intrinsic subtypes, risk of recurrence proliferation (RORP), and MammaPrint, were also tested for associations with pCR. RNA-Seq data was also used to identify ED-predictive genes. Differential expression was assessed in normalized RNA-Seq data using DESeq2 and each sample was subtyped with the AIMS classifier. Wilcoxon two-sided test, chi-square, or Fisher's exact tests were used to assess associations with pCR.

Results: Subtypes were determined with RNA-Seq data from pretreatment biopsies (N=230). The 8-gene T-benefit signature was associated with pCR. The high-, medium-, and low- T-benefit groups had pCR rates of 55%, 44%, and 6.8%, respectively (p=1.3e-13). Intrinsic subtypes were associated with pCR by comparing HER2E to all other subtypes combined (69% v 28%, p=3.9e-08). Hot spot mutations in PIK3CA alone (p=0.014), or combined with hot spot mutations in ERBB2, ERBB3, AKT1, PTEN, and MAP3K1, were associated with no pCR (p=0.0007) and may be useful as resistance markers. sTILs, MammaPrint, RORP, and some immune cell signatures also showed statistically significant associations with pCR but did not identify a subset of pts with an increased pCR rate in the TCHP + ED arm. In contrast, expression of the SH3BP2 gene was associated with pCR only in the TCHP + ED arm (interaction p=0.03).

Conclusion: The previously validated 8-gene T-benefit signature identifies a subset of pts with very low pCR rate (6.8%) with TCHP. PIK3CA and other activating mutations were associated with no pCR. These findings may identify pts with resistant disease who may require a different treatment. Exploratory analyses suggest that SH3BP2 expression may identify pts who may benefit from TCHP + ED, but validation is required for clinically utility.

Support: BCRF, U10CA180868, -180822; UG1CA189867, Genentech, PUMA Biother

Citation Format: Katherine L. Pogue-Geile, Ying Wang, Huichen Feng, Corey Lipchik, Rim S. Kim, Reena S. Cecchini, Samuel A. Jacobs, Ashok Srinivasan, Joseph P. Costantino, Eleftherios P. Mamounas, Charles E. Geyer, Priya Rastogi, Peter C. Lucas, Soonmyung Paik, C. Kent Osborne, Norman Wolmark, Mothaffar F. Rimawi. Association of molecular signatures, mutations, and sTILs, with pCR in breast cancer patients in NRG Oncology/NSABP B-52 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4064.

Abstract 2257: Phase II study of dual immune checkpoint blockade (ICB) with durvalumab (Durva) plus tremelimumab (T) following palliative hypofractionated radiotherapy (SBRT) in patients (pts) with microsatellite-stable (MSS) metastatic colorectal cancer (mCRC) progressing on chemotherapy: NSABP FC-9

Background

Monotherapy with ICB has not been effective in MSS mCRC. Preclinical data demonstrate that immunomodulators synergize with radiotherapy (RT) resulting in tumor regression at irradiated sites and rarely at non-irradiated sites. Anecdotal reports in pts have confirmed an abscopal effect of RT and ICB. This phase II, open-label, single-arm study is testing dual ICBs following SBRT in pts with MSS mCRC who have progressed on chemotherapy. We report here efficacy and safety results.

Methods

Eligible pts have: MSS mCRC, progressed on prior oxaliplatin and irinotecan-based regimens, measurable lesions with at least one amenable to SBRT and another for core biopsy, and performance status &lt;2. Following 3 doses of SBRT at 9 Gy daily (D −2, −1, and D 0 prior to Cycle 1), pts received the combination of T (75 mg IV infusion) and Durva (1500 mg IV infusion) on D 1 of Cycles 1-4. Beginning with Cycles 5-12, pts received Durva alone on D 1 q 28d. Pts were considered evaluable using RECIST 1.1 if a tumor response at non-irradiated target lesions was measured at baseline and after 2 cycles. Subsequent scans were performed every 8 wks. Toxicity was graded according to NCI CTCAE v4.0. Primary aim is to determine overall objective response rate (ORR) in non-irradiated metastasis. Secondary aims are clinical benefit rate, duration of response, tolerability, and correlates of response. Archived and fresh tumor biopsies were obtained at study entry and after cycle 2, blood samples were collected before treatment, at cycle 1 D 15, and on D 1 of cycles 2, 4, and 6.

Results

FC-9 is open at six academic centers. From October 2017 to November 1, 2018, 33 pts enrolled with 20 pts evaluable. Median age was 58 y (range, 37-71). Toxicity was assessed without regard to attribution. One pt had grade 5 unexplained sudden death (3%); two had grade 4 (6%, colitis, dehydration, pneumonitis); and 12 had grade 3 (38%, primarily GI, other than colitis, and nutrition). Partial responses were seen in 2 pts lasting 44 wks and 44+ wks; two pts had stable disease of 12 and 16 wks duration. Correlative studies will be presented including PD-L-1 expression, CD8+ T cell infiltration into tumor tissues, and gene expression of immune pathways.

Conclusions

The combination of SBRT and dual immunotherapy was safe and well tolerated following immunotherapy standard guidelines. In this refractory group of MSS mCRC pts, we observed 2 partial responses of 44 and 44+ wks among 20 evaluable pts. Correlative analyses will be presented.

Support: Astra-Zeneca; NSABP Foundation, Inc.

Citation Format: James J. Lee, Greg Yothers, Thomas J. George, Marwan G. Fakih, Atrayee Basu Mallick, Edith P. Mitchell, James L. Wade, John C. Krauss, Omar R. Kayaleh, Dwight E. Heron, Carmen J. Allegra, Corey Lipchik, Huichen Feng, Marion Joy, Ashok Srinivasan, Katherine L. Pogue-Geile, Peter C. Lucas, Sarah E. Warren, Alessandra Cesano, Samuel A. Jacobs. Phase II study of dual immune checkpoint blockade (ICB) with durvalumab (Durva) plus tremelimumab (T) following palliative hypofractionated radiotherapy (SBRT) in patients (pts) with microsatellite-stable (MSS) metastatic colorectal cancer (mCRC) progressing on chemotherapy: NSABP FC-9 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2257.

Abstract 1923: KRAS-mutant (mt) colorectal cancer (CRC) organoid models generated from patient-derived xenografts (PDX) show response to combination of trametinib (Tm), neratinib (N), and trastuzumab (Tz)

Background: KRAS-mt CRC has constitutively activated RAF-MEK-ERK pathways and resistance to anti-EGFR therapies. In pre-clinical models, we found that cells with inflammatory subtype tumors were sensitive to the MEK-inhibitor, MEK162, plus N, regardless of KRAS mutations. However, both KRAS-mt and -wt stem-like CRC cells were resistant to this combination. In C-07 and C-08 clinical studies, patients (pts) with stem-like subtype tumors were resistant to chemotherapy and had a very poor prognosis. We hypothesized that dual-HER2 targeting may provide more robust ERBB inhibition than N alone. We therefore tested Tz combined with Tm+N using PDX organoids (PDXOs) derived from KRAS-mt CRC tumors. PDOs have emerged as powerful preclinical models to predict clinical outcomes. The goal of this study was to identify more efficacious drug combinations for KRAS-mt tumors and stem-like subtype tumors using PDXOs.

Methods: PDXO’s were generated using recently described methods from Hans Clevers' laboratory. Three KRAS-mt PDX tissues from Champions Oncology were used to generate four PDXOs for drug testing. The CTG-0406 PDX model was used to develop PDXOs from two different mice.

Results: All three KRAS-mt PDXOs: CTG-0406 (inflammatory), CTG-1170 (inflammatory), and CTG-0079 (stem-like), were resistant to Tm, N, and Tz, as single agents. N+Tz was effective in inhibiting cell viability in all four models; however, more significant viability inhibition occurred when Tm was added to N+Tz in three of the PDXOs including the stem-like model. In all PDXOs, Tm+N+Tz inhibited 67-76% viability.

Conclusion: We demonstrate that KRAS-mt PDXOs were inhibited to a greater extent with Tm+N+Tz compared to any of these drugs alone. PDXOs provide a rapid and cost-effective preclinical platform for screening of unique drug combinations for sensitivity or resistance.

Table 1.% PDXO cell viabilityDrugsCTG-0406 (1) (KRAS mt) InflammatoryCTG-0406 (2) (KRAS mt) InflammatoryCTG-1170 (KRAS mt) InflammatoryCTG-0079 (KRAS mt) Stem-LikeTm (10nM)96%116%95%94%N (125nM)109%97%96%92%Tz (20 µg/ml)92%119%97%93%Tm (10nM) + N (125nM)64%59%31%56%Tm (10nM) + Tz (20 µg/ml)74%75%41%70%N (125nM) + Tz (20 µg/ml)34%70%23%43%Tm (10nM) + N (125nM)+ Tz (20 µg/ml)26%33%24%31%

Support: NSABP Foundation, Inc.

Citation Format: Rekha Pal, Ashok Srinivasan, Peter C. Lucas, Carmen J. Allegra, Angela M. Davies, Alshad S. Lalani, Samuel A. Jacobs, Katherine L. Pogue-Geile. KRAS-mutant (mt) colorectal cancer (CRC) organoid models generated from patient-derived xenografts (PDX) show response to combination of trametinib (Tm), neratinib (N), and trastuzumab (Tz) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1923.

Biomarker analysis of PALLET: A neoadjuvant trial of letrozole (L) ± palbociclib (P)

570

Background: PALLET randomized 307 postmenopausal women with ER+ primary breast cancer to one of 4 treatment groups (3:2:2:2 ratio): A: L for 14wks; B: L for 2wks then L+P to 14wks; C: P for 2wks then L+P to 14wks; D: L+P for 14wks. This allowed a randomized 1:2 comparison of L (Group A) vs L+P (Groups B+C+D) at 14wks. P was given 125mg/d PO (21 days on, 7 days off). Adding P to L markedly enhanced Ki67 suppression and Complete Cell Cycle Arrest (CCCA, Ki67 < 2.7%) by 14wks but did not substantially increase clinical response. We now report exploratory analysis of the association of baseline expression of 6 pre-specified biomarkers involved in estrogen and CDK4/6 signaling with CCCA at 14wks and changes in their expression during therapy. Methods: Estrogen receptor (ER), progesterone receptor (PgR), RB and CCNE1 were measured by IHC and CCND1 by IHC and FISH (CCND1/CEP11 ratio≥2.0 amplified). Baseline biomarker values were available with 14wk Ki67 values in up to 64 patients for L alone and up to 124 patients for L+P. Of these 59% and 90%, respectively, achieved CCCA. Results: With L alone CCCA was significantly less frequent (indicating relative resistance) with low baseline PgR (odds ratio [OR] 0.22, 95%CI 0.05-0.96, p = 0.04) or high CCNE1 levels (OR 10.39, 95%CI 1.19-90.48, p = 0.03). With L+P CCCA was also significantly less frequent with high CCNE1 (OR 50.34 95%CI 5.12-495.34, p = 0.001) or with low baseline ER (OR 0.21 95%CI 0.08-0.60, p = 0.004). CCCA was not significantly different with either treatment according to CCND1 amplification status or expression overall. However, CCCA showed a tendency to being less frequent in non-amplified cases with low baseline cyclin-D1 expression when treated with L+P (p = 0.10). There were no significant changes in ER levels or CCND1 amplification over 14wks. By 14 wks PgR, RB, CCND1 and CCNE1 levels were significantly suppressed by L or L+P (geomeans PgR: -96.4% vs -94.9%; CCND1: -79.9% vs -70.7%; CCNE1: -68.2% vs -74.7%; RB: -23.5% vs 26.1%, respectively) and there was no significant difference between the treatments. Conclusions: These data support low ER, possibly indicating limited luminal status, and high CCNE1 as markers of poor Ki67 response to L+P in primary disease and are consistent with findings in studies in advanced disease. Clinical trial information: NCT02296801.