Statistical modeling of a novel clinical trial design using neoadjuvant therapy (NAT) to personalize therapy in patients (pts) with triple-negative breast cancer (TNBC)

595

Background: 40-50% of pts with TNBC develop pathologic complete response (pCR) with adriamycin/cyclophosphamide (AC)àtaxane (T) NAT; thus, most pts treated in randomized trials (RCTs) adding experimental drugs (ED) to standard NAT do not benefit from trial participation. A personalized trial design that enriches for non-pCR to standard NAT would diminish toxicity from ED in pts who do not need them and enrich ED in high-risk pts that are most likely to benefit. Methods: ARTEMIS (NCT02276443) is a non-randomized trial to study personalization of NAT in TNBC. Tumor biopsies were performed pre-NAT and volumetric change by ultrasound (VCU) after 4 cycles of AC (or upon clinical progression) assessed response. Pts with sensitive TNBC (VCU >=70% after AC) had T as the second phase of NAT. Pts with <70% VCU were offered phase II trials. pCR was assessed at surgical resection. 273 pts had available pCR status and 222 had complete data to generate a model predictive of response using multivariate logistic regression with common clinical factors. Data was randomly divided into training (n=111) and validation (n=111) sets. Results: 85 pts (38%) had pCR and VCU after AC x 4 was the strongest predictor of pCR. Other factors significant on multivariate analysis and included in the model were T stage (T1-4), stromal TIL, Ki67 and PD-L1. When applied to the validation data set, the accuracy of this model for predicting pCR was 76.6%, sensitivity 78.6% and specificity 75.4%. The PPV was 66.0% and the NPV was 85.2% with a ROC curve AUC of 82.4%. Using these data, ED exposure (table) was estimated for the ARTEMIS study design vs a 1:1 or a 2:1 RCT design (with an estimated pCR in control arm=40%), with a demonstrated benefit for personalization. Conclusions: This modeling indicates that personalization of NAT trials has the potential to enrich ED exposure for non-responsive disease as well as diminish ED exposure in pts likely to achieve pCR with standard NAT. Improved prediction of pCR would further enhance personalized trial design. Clinical trial information: NCT02276443 . [Table: see text]

Comprehensive profiling of androgen receptor-positive (AR+) triple-negative breast cancer (TNBC) patients (pts) treated with standard neoadjuvant therapy (NAT) +/- enzalutamide

517

Background: The luminal androgen receptor (LAR) subtype of TNBC has a low pathologic complete response (pCR) rate after NAT. We determined the pCR rate of the enzalutamide and paclitaxel (ZT) regimen for pts with anthracycline-insensitive AR+ TNBC (NCT02689427), and related biomarkers. Methods: ARTEMIS (NCT02276443) is a non-randomized trial to determine if NAT can be used to personalized therapy. Pts received 4 cycles of doxorubicin-based NAT (AC). Pts with insensitive disease by imaging were offered clinical trials as the second phase of NAT based upon molecular profiling of pre-treatment biopsies. Immunohistochemistry (IHC) of AR+≥10% was the threshold for selecting ZT (enzalutamide 160 or 120 mg PO qD + paclitaxel 80 mg/m2 qW for 12 cycles). pCR was determined by surgery after NAT. Trial had two-stage Phase II design, and we report the completed first stage. We evaluated the concordance between Vanderbilt LAR subtype by molecular profiling (microarray and RNAseq) and IHC %AR+ cells. Frequency of PI3K pathway alterations within the LAR subtype was assessed. Results: 267 pts had tumors profiled by IHC, 220 by microarray, 187 by RNAseq and 197 by whole exome sequencing. 96 pts had post-AC RNAseq. LAR scores from both RNAseq and microarray profiling (n = 139) were highly concordant (R = 0.89, P < 0.001) and identified ~10% of TNBCs tested as LAR. The %AR+ cells from IHC correlated with LAR subtype scores according to RNAseq (R = 0.6, P < 0.001), with a cut-point of ≥30% AR+ having the best concordance with LAR subtype. Unlike other subtypes, by serial profiling, LAR TNBCs did not change subtype signatures after exposure to AC. LAR TNBCs had low rates of pCR (23%) and high rates of PI3K pathway activating aberrations (85%); however PI3K aberrations did not correlate with pCR. Seventeen patients with AC-insensitive TNBC received ZT. Five of 15 patients (33.3%) had responses (pCR or RCB-I). Toxicities are Grade (Gr) 4 syncope (n = 1), Gr3 abnormal liver function (n = 2), Gr3 neutropenia (n = 4). IHC & LAR subtype scores did not statistically associate with response to ZT (P = 0.8, P = 0.9). However, all responders to ZT had an upregulated androgen response pathway (ssGSEA Z > 1) as measured by transcriptomic analysis in pre-treatment biopsies analysis (P = 0.05, ppv = 0.56, npv = 1). Conclusions: The LAR TNBC subtype has a low pCR rate to NAT. Among pts with AC-insensitive TNBC, baseline upregulated androgen response pathway and LAR subtype may benefit from the ZT regimen, potentially by PI3K targeting. Clinical trial information: NCT02689427 .

Immune phenotype and response to neoadjuvant systemic therapy (NAST) in triple negative breast cancer (TNBC)

509

Background: In TNBC patients (pts) receiving NAST, increasing tumor infiltrating lymphocytes (TILs) is associated with higher pathologic complete response (pCR) rates. However, since the presence of TIL do not consistently predict pCR, the current study was undertaken to more fully characterize the immune cell response and its association with pCR. Methods: T cell receptor (TCR) sequencing, PD-L1 immunohistochemistry and multiplex immunofluorescence were performed on prospectively collected pre-NAST tumor samples from 98 pts with stage I-III TNBC enrolled in ARTEMIS (NCT: 02276443). TCR clonality was calculated using Shannon’s entropy. PD-L1+ was defined as ≥1% immune cell staining. Response to NAST was defined using the residual cancer burden (RCB) index. Associations between TCR clonality, immune phenotype, and response were examined with the Wilcoxon rank sum test, Spearman’s rank correlation and multivariable logistic regression using stepwise elimination (threshold p > 0.2), as appropriate. Results: The pCR rate was 39% (38/98). pCR was associated with higher TCR clonality (median = 0.2 [in pts with pCR] vs 0.1 [in pts with residual disease], p = 0.05). Notably, the association between pCR and higher TCR clonality was observed in pts with ≥5% TIL (n = 61; p = 0.05) but not in pts with < 5% TIL (n = 37; p = 0.87). Among pts with ≥5% TIL, TCR clonality emerged as the only independent predictor of response in a multivariable model of tumor immune characteristics (odds ratio/0.1 increase in TCR clonality: 3.0, p = 0.021). PD-L1+ status was associated with higher TCR clonality (median = 0.2 [in PD-L1+] vs 0.1 [in PD-L1-], p = 0.004). Higher TCR clonality was associated with higher CD3+ (rho = 0.32, p = 0.0018) and CD3+CD8+ (rho = 0.33, p = 0.0013) infiltration but lower expression of PD-1 on CD3+ (rho = -0.24, p = 0.021) and CD3+CD8+ cells (rho = -0.21, p = 0.037). Conclusions: In TNBC, a more clonal T cell population is associated with an immunologically active microenvironment (higher CD3+ and CD3/8+ T cell; lower PD-1+CD3+ and PD-1+CD3/8+ T cell; PD-L1+) and favorable response to NAST, especially in pts with ≥5% TIL, suggesting a role for deep immune phenotyping in further refining the predictive value of TILs.

Phase II study of copanlisib in patients with tumors with PIK3CA mutations (PTEN loss allowed): NCI MATCH EAY131-Z1F

3506

Background: The NCI-MATCH (EAY131) is a platform trial that enrolls patients (pts) with solid tumors, lymphomas, or multiple myeloma to targeted therapies based on matching genomic alterations of interest (NCT02465060). Arm Z1F evaluated copanlisib, a highly selective, pan-Class 1 PI3K inhibitor with predominant activity against both the δ and α isoforms in pts with PIK3CA mutations. Methods: Pts received copanlisib (60 mg IV) on days 1, 8, and 15 in 28-day cycles until progression/toxicity. Tumor assessment was every 2 cycles. The primary endpoint was objective response rate (ORR); secondary endpoints were PFS, 6-month PFS, and predictive biomarkers. Pts with KRAS mutations, HER2+ve breast cancers, lymphomas were excluded. Results: 35 pts were enrolled (from 8/2/18 to 12/27/18), of which, 28 pts were available for analysis (7 patients, not eligible or did not start therapy). Multiple histologies were enrolled with gynecologic (n = 7), gastrointestinal (n = 6), and genitourinary (n = 5) the most common tumors. Median age 61 (range 42-78). 75% of pts had ≥ 3 lines of prior therapy. 54% of PIK3CA mutations were located in the helical domain, 32% in kinase domain and 14% in other domains. Twenty-six pts had co-occurring gene alterations (median 3; range 1-9), with 9 patients having 4 or more gene alterations. The ORR was 11% (3/28, 90% CI: 3%-25%). Partial responses were seen in uterine cancer, clear cell carcinoma of anterior abdominal wall, and liposarcoma. 6 pts had > 6 months of stable disease and clinical benefit rate was 32% (9/28). Two pts are still on treatment. The most common reason for protocol discontinuation was disease progression (n = 18, 69%). Thirty pts were included for toxicity analysis. Ten pts (33%) had grade 1 or 2 toxicities, 16 pts (53%) had grade 3 toxicities, and one patient (3%) had grade 4 toxicity (CTCAE v5.0). Most common toxicities include hyperglycemia (n = 19), fatigue (n = 11), hypertension (n = 10), diarrhea (n = 10), and nausea (n = 9). Total of 5 deaths were reported, none related to treatment. Conclusions: Copanlisib showed meaningful clinical activity across various tumors with PIK3CA mutation in the late-line refractory setting. Further study either alone or in combinations in select tumors is warranted. G3/4 toxicities observed were consistent with reported toxicities for PI3K pathway inhibition. Clinical trial information: NCT02465060 .

Incidence of PI3K pathway alteration and response to neoadjuvant therapy (NAT) in triple negative breast cancer (TNBC) subtypes

561

Background: Limited cell line and human data suggest that TNBCs characterized as mesenchymal and luminal androgen receptor (LAR) commonly have alterations in the PI3K pathway. More data is needed to better characterize the role of the PI3K pathway across TNBC subtypes. Methods: Pre-treatment tumor biopsies were collected from operable TNBC patients (pts) enrolled on a clinical trial of genomically tailored NAT (ARTEMIS; NCT02276443). Tumors were categorized into 5 groups using the Pietenpol criteria: basal-like (BL) comprised of BL-1 and BL-2, mesenchymal and mesenchymal stem-like (M), immunomodulatory (IM), LAR, or unspecified (UNS). Using whole exome sequencing data, variants (single nucleotide polymorphisms and insertions/deletions) and copy number variations (CNVs) were identified in 32 genes known to activate the PI3K pathway. Results: Tumor subtyping and pathologic response to NAT was available in 127 pts (clinical stage I: 9; II: 84; III: 34). PI3K pathway alteration defined as a variant in one of the evaluated genes and/or deletion of PTEN was seen in 76 (60%) tumors. The most frequent alterations were: PTEN deletion (21%), PIK3CA variant (11%), and PIK3R1 variant (8%). PI3K alteration and residual cancer burden (RCB) rates across TNBC subtypes are shown in the table. There was a significant difference in pathologic complete response (pCR)/RCB 0 rate after NAT across TNBC subtypes (chi2 test; P = 0.02). There was a significant difference in the incidence of PI3K pathway alteration across TNBC subtypes (chi2 test; P < 0.01). Overall, the presence of PI3K alteration was not associated with pCR (Fisher exact test; P = 0.85). Pts with M tumors had a higher rate of substantial residual disease (RCB II-III) after NAT. Presence of PI3K pathway alteration was common in the M subtype and associated with RCB II-III (82% in PI3K-altered vs 33% in wild-type tumors; Fisher exact test; P = 0.02). Presence of PI3K pathway alteration was common but not associated with response in the LAR subtype. Conclusions: The incidence of PI3K pathway alteration varied by TNBC subtype but was not associated with pathologic response to NAT with the exception of increased substantial residual disease (RCB II-III) in the M subtype. [Table: see text]

Abstract P2-16-09: Residual cancer burden in patients with early stage triple negative breast cancer who progress on anthracycline-based neoadjuvant chemotherapy in an ongoing clinical trial (ARTEMIS)

BACKGROUND: Current treatment for early stage triple negative breast cancer (TNBC) includes neoadjuvant systemic chemotherapy (NAST), which is used to assess disease biology and the need for adjuvant treatment in case of residual disease at the time of surgery, also known as residual cancer burden (RCB). Patients with TNBC who experience RCB-0 (pathologic complete response [pCR]) or RCB-I after NAST have an excellent prognosis whereas patients with significant residual disease (RCB-II or RCB-III) are at a high risk of relapse. Standard NAST for TNBC achieves pCR in 30-50% of cases. NAST typically consists of anthracycline-based chemotherapy followed or preceded by a taxane +/- carboplatin. Disease progression (PD) is uncommon in TNBC patients receiving NAST and little is known regarding outcomes in patients who have PD during the initial phase of NAST. METHODS: Total 316 TNBC patients were evaluated from two prospectively accrued clinical trials of NAST (NCT02276443 and NCT01334021). The ARTEMIS trial (NCT02276443) aims to improve pCR rates by adding targeted therapy to chemotherapy as the second phase of NAST for those patients who do not experience at least a 70% volumetric reduction after 4 cycles of doxorubicin/cyclophosphamide (AC). Unique histopathologic features including % stromal tumor-infiltrating lymphocytes (sTIL), presence of mesenchymal histology (high vimentin expression by IHC), and androgen receptor expression are used to guide second phase therapy. RESULTS: 31 TNBC patients had PD while receiving AC as the first phase of NAST (10%; 95% CI= 6.69-13.31%). 9 of 31 patients proceeded to standard chemotherapy and all had RCB II/III disease. 22 of 31 patients were enrolled to targeted therapy trials. 6 were treated with the EGFR inhibitor panitumumab + carboplatin/paclitaxel, 9 with atezolizumab + nab-paclitaxel, and 7 with everolimus, bevacizumab, and liposomal doxorubicin (DAE). Of these 22 patients, 3 (13.6%) had pCR/RCB-0, 1 (4.5%) RCB-I and 18 (81.8%) had RCB II/III. All 4 patients who experienced RCB-0/I had T2N0 disease at diagnosis. 2 had sTIL &lt; 5% and 2 patients had 70% sTIL. CONCLUSION: PD is uncommon while receiving NAST. Patients with TNBC and progression on initial NAST with AC are unlikely to achieve pCR or RCB-I status despite subsequent standard chemotherapy. Combination chemotherapy with targeted therapy on clinical trial resulted in a numerically higher rate of pCR+RCB-I (18%) as salvage therapy, but this was not statistically significant and requires confirmation in larger trials.

Citation Format: Haven Garber, Gaiane Rauch, Beatriz Adrada, Rosalind Candelaria, Elizabeth Mittendorf, Alastair Thompson, Jennifer Litton, Senthil Damodaran, Bora Lim, Banu Arun, Naoto Ueno, Vicente Valero, Nuhad Ibrahim, Rashmi Murthy, Debu Tripathy, Helen Piwnica-Worms, Fraser Symmans, Lei Huo, Stacy Moulder. Residual cancer burden in patients with early stage triple negative breast cancer who progress on anthracycline-based neoadjuvant chemotherapy in an ongoing clinical trial (ARTEMIS) [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 P2-16-09.

Abstract P6-02-03: Quantitative apparent diffusion coefficient (ADC) radiomics of tumor and peritumoral regions as potential predictors of treatment response to neoadjuvant chemotherapy (NACT) in triple negative breast cancer (TNBC) patients

Background and Purpose: TNBC is comprised of biologically aggressive tumors with diverse clinical behavior and response to chemotherapy. Prediction of disease response to NACT is critical to the development of personalized medicine in TNBC. We evaluated first-order radiomic features from quantitative ADC maps of the tumor and peritumoral region as discriminators of response to NACT in TNBC patients.

Materials and Methods: This IRB-approved prospective study (ARTEMIS trial, NCT02276443) included 34 patients with biopsy proven stage I-III TNBC who underwent evaluation of treatment response by multi-parametric MRI. Patients had a baseline MRI (BL) and a second MRI after 4 cycles (C4) of their treatment. After completion of NACT, all patients underwent surgery and were classified as pathologic complete response (pCR) or non-pCR.

Both MRI exams included T2W series, a dynamic contrast enhanced series (DCE), a conventional diffusion weighted imaging (DWI) series, and a reduced field of view (rFOV) DWI series. Tumor volumes were contoured by an experienced breast radiologist on ADC maps with reference to b1000 DWI images. Regions with necrosis or clip artifacts were excluded from the contour. Peritumoral regions were defined as a 5 mm rim of tissue surrounding the tumor based on DCE series, T2-weighted images with fat suppression and ADC maps. Thirteen first-order radiomic features, including mean, minimum, maximum, percentiles, kurtosis and skewness at a single measurement and the difference between BL and C4 were compared between pCR and non-pCR using Receiver Operating Characteristic (ROC) curve and Wilcoxon rank sum test.

Results: The kurtosis of tumor at C4 by conventional DWI was significantly higher in non-pCR than in pCR patients (AUC=0.785, p=0.0097). The change in kurtosis from BL to C4 by conventional DWI was also significantly higher in non-pCR than in pCR patients (AUC=0.73, p=0.043). The skewness of tumor at C4 by rFOV DWI scan was significantly lower in pCR than non-pCR patients (AUC=0.73, p=0.023).

The 10th percentile of the peritumoral region’s ADC was significantly different between pCR and non-pCR (mean=1.19, SD is ± 0.27 10-3 mm2/s vs mean=1.34, SD ± 0.27 10-3 mm2/s respectively, AUC=0.70, p=0.048). The kurtosis and 25th percentile of the ADC of peritumoral region were borderline significantly different between pCR and non-pCR (AUC=0.69, p=0.067; AUC=0.69, p= 0.073 respectively).

Conclusion: ADC first-order radiomic features from tumor and peritumoral region in TNBC may be useful for predicting treatment response to NACT. Larger study is necessary and is currently in progress to validate these findings.

Citation Format: Beatriz E. Adrada, Abeer H. Abdelhafez, Benjamin C. Musall, Kenneth R. Hess, Jong Bum Son, Mark D. Pagel, Ken-Pin Hwang, Rosalind P. Candelaria, Lumarie Santiago, Gary J. Whitman, Huong Le-Petross, Tanya W. Moseley, Elsa Arribas, Deanna L. Lane, Marion E. Scoggins, David A. Spak, Jessica W.T. Leung, Senthil Damodaran, Bora Lim, Vicente Valeo, Jason B White, Alastair M. Thompson, Jennifer K. Litton, Stacy L. Moulder, Jingfei Ma, Wei T. Yang, Gaiane M Rauch. Quantitative apparent diffusion coefficient (ADC) radiomics of tumor and peritumoral regions as potential predictors of treatment response to neoadjuvant chemotherapy (NACT) in triple negative breast cancer (TNBC) patients [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 P6-02-03.

Abstract OT2-07-01: A phase 2 study of futibatinib (TAS-120) in metastatic breast cancers harboring fibroblast growth factor receptor (FGFR) amplifications (FOENIX-MBC2)

Background: FGFR1 gene amplifications occur in ~15% of invasive breast cancers (BCs) andhave been shown to be associated with endocrine therapy resistance, whereas FGFR2 amplifications occur in ~2% of invasive BCs (4% of triple-negative BCs [TNBCs]). Futibatinib is an oral, highly selective, irreversible FGFR1-4 inhibitor that has been shown to inhibit both mutant and wild-type FGFR isoforms. In a phase 1 study, futibatinib showed promising clinical activity and tolerability across tumor types, including BC. This phase 2 trial (FOENIX-MBC2) is designed to evaluate futibatinib alone or in combination with fulvestrant (a selective estrogen receptor down-regulator administered intramuscularly) in patients with metastatic BC.

Trial design: FOENIX-MBC2 is a multicenter, phase 2, open-label, non-randomized study planned to be conducted in patients with locally advanced/metastatic BC harboring FGFR1/2 amplifications who have experienced disease progression after prior therapy for advanced/metastatic disease. Eligibility criteria include an Eastern Cooperative Oncology Group performance status of 0 or 1 and no prior FGFR inhibitor treatment. Approximately 168 patients are planned to be enrolled in one of four cohorts based on a recurrent BC diagnosis and FGFR amplification status (table) as determined by local testing. Patients will receive single-agent futibatinib (cohorts 1-3) or futibatinib plus fulvestrant (cohort 4) until disease progression, unacceptable toxicity, or other discontinuation criteria are met. Primary and secondary endpoints are detailed in the table. Sample sizes for cohorts 1, 2, and 3 are based on a Simon’s optimal 2-stage design; that for cohort 4 is based on a proof-of-concept phase 2 design. The anticipated start date is August 30, 2019.

Patients, treatment, and endpoints in cohorts 1-4 of FOENIX-MBC2

CohortApprox. target enrollment (n)TreatmentKey patient inclusion criteriaEndpointsa1≤55FutibatinibHR+ HER2– BC, measurable disease per RECIST v1.1, FGFR2 amplification, and 1–3 prior endocrine therapies and ≤2 prior chemotherapy regimens for advanced/metastatic diseasePrimary: ORR Secondary: CBR, DOR, OS, PFS, 6-month PFS rate, safety2≤55FutibatinibTNBC, measurable disease per RECIST v1.1, FGFR2 amplification, and ≥1 prior chemotherapy or chemotherapy/immunotherapy regimen for advanced/metastatic diseasePrimary: ORR Secondary: CBR, DOR, OS, PFS, 6-month PFS rate, safety3≤24FutibatinibHR+ HER2– BC or TNBC; non-measurable, evaluable disease; FGFR2 amplification; and prior therapy as per cohort 1 (HR+ HER2– BC) or cohort 2 (TNBC)Primary: CBR Secondary: CR rate, DOR, OS, PFS, 6-month PFS rate, safety4≤34Futibatinib + fulvestrantHR+ HER2– BC, measurable disease per RECIST v1.1, high levels of FGFR1 amplification (FGFR1:CEN8 ratio ≥5.0 or FGFR1 copy number ≥10), and 1–2 prior endocrine-containing regimens and ≤1 prior chemotherapy regimen for advanced/metastatic disease, but no prior fulvestrantPrimary: 6-month PFS rate Secondary: ORR, CBR, DOR, OS, PFS, safetyCBR, clinical benefit rate; CR, complete response; DOR, duration of response; HER2-, human epidermal growth factor-negative; HR+, hormone-receptor-positive; ORR, objective response rate; OS, overall survival; PFS, progression-free survival; RECIST v1.1, Response Evaluation Criteria in Solid Tumors version 1.1aORR is defined as the proportion of all treated patients with a best overall response of CR or PR; CBR is defined as the proportion of all treated patients with a best overall response of CR, PR, or SD ≥24 weeks. ORR and CBR will be summarized descriptively. The 6-month PFS rate is the percentage of patients who remain alive and progression-free at 6 months estimated using the Kaplan-Meier method.

This study is funded by Taiho Oncology, Inc. and Taiho Pharmaceutical Co., Ltd.

Citation Format: Nick C. Turner, Ian E. Krop, Aditya Bardia, Senthil Damodaran, Miguel Martin, Karim A. Benhadji, Yaohua He, Mieke Ptaszynski, Carlos L. Arteaga. A phase 2 study of futibatinib (TAS-120) in metastatic breast cancers harboring fibroblast growth factor receptor (FGFR) amplifications (FOENIX-MBC2) [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 OT2-07-01.

Abstract P1-10-20: Serial TILs: Evaluating the role of mid-treatment tumor infiltrating lymphocytes (TIL) in predicting pathologic complete response (pCR) in early-stage triple negative breast cancer (TNBC)

Introduction High levels of TIL at baseline are associated with higher pCR rates and better overall survival in TNBC. Recent studies have also indicated that higher TIL in post-NACT residual disease in TNBC are an important independent predictor of improved survival. We evaluated the role of mid-treatment (post-AC; Adriamycin/Cyclophosphamide) TIL in predicting pCR rates in early-stage TNBC. Methods Of 242 patients with stage I-III TNBC enrolled in the ARTEMIS trial (NCT02276443), 156 patients had pre-AC TIL and pCR status available for this analysis. Both pre-and post-AC TIL counts were available in 29 patients. Post-AC TIL counts for the remaining patients were imputed using linear regression with age, race, stage III, vimentin &gt;50% and post-AC tumor volume reduction. Using these imputed TIL counts we evaluated the association of post-AC TIL with pCR. We also evaluated the change in TIL before and after treatment with AC. Results At baseline the median TIL count was 10% (n=156). In the post-AC samples, the median TIL count was 5%. Using imputed TIL counts, we did not conclude that post-AC TIL was associated with pCR (p= 0.28). Using a cut-point of 15% TIL, our analysis showed that baseline TIL is more strongly correlated with pCR than post-AC TIL (Table 1). In our univariable logistic regression, both baseline TIL and the difference in TIL pre-and post- treatment were significantly associated with pCR (p= 0.0015 and p=0.0068, respectively), however in the multivariable analysis only baseline TIL was significant. Our analysis did show that a decrease in TIL from pre- to post-treatment was significantly associated with pCR (p=0.022). However, this measure was not significant in our logistic regression model when pre-TIL was also included. Conclusion Higher pre-treatment TIL correlated more strongly with pCR rate when compared to post-AC TIL. Pre-treatment high TIL was associated with pCR regardless of changes in TIL pre and post treatment.

Table 1. Changes in TIL before and after treatmentBaseline TILPost-AC TILN#pCR (%)LowLow6217 (27%)LowHigh4012 (30%)HighLow2513 (52%)HighHigh2916 (55%)TIL; Low: &lt;15, High &gt;15

Citation Format: Nour Abuhadra, Kenneth Hess, Jennifer Litton, Gaiane Rauch, Alastair Thompson, Bora Lim, Beatriz Adrada, Elizabeth Mittendorf, Senthil Damodaran, Rosalind Candelaria, Banu Arun, Wei Tse Yang, Naoto Ueno, Lumarie Santiago, Rashmi Murthy, Nuhad Ibrahim, Sahin Aysegul, William Symmans, Lei Huo, Stacy Moulder. Serial TILs: Evaluating the role of mid-treatment tumor infiltrating lymphocytes (TIL) in predicting pathologic complete response (pCR) in early-stage triple negative breast cancer (TNBC) [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 P1-10-20.

Phase II study of Radium-223 dichloride combined with hormonal therapy for hormone receptor-positive, bone-dominant metastatic breast cancer

Background

Radium‐223 dichloride (Ra‐223) is a targeted alpha therapy that induces localized cytotoxicity in bone metastases. We evaluated the efficacy and safety of Ra‐223 plus hormonal therapy in hormone receptor‐positive (HR+), bone‐dominant metastatic breast cancer.

Methods

In this single‐center phase II study, 36 patients received Ra‐223 (55 kBq/kg intravenously every 4 weeks) up to 6 cycles with endocrine therapy. The primary objective was to determine the clinical disease control rate at 9 months. Secondary objectives were to determine (a) tumor response rate at 6 months, (b) progression‐free survival (PFS) durations, and (c) safety.

Results

The median number of prior systemic treatments for metastatic disease was 1 (range, 0‐4). The disease control rate at 9 months was 49%. The tumor response rate at 6 months was 54% (complete response, 21%; partial, 32%). The median PFS was 7.4 months (95% CI, 4.8‐not reached [NR]). The median bone‐PFS was 16 months (95% CI, 7.3‐NR). There were no grade 3/4 adverse events.

Conclusions

Ra‐223 with hormonal therapy showed possible efficacy in HR+ bone‐dominant breast cancer metastasis, and adverse events were tolerable. We plan to further investigate the clinical application of Ra‐223 in these patients. (NCT02366130).

Neoadjuvant Talazoparib for Patients With Operable Breast Cancer With a Germline BRCA Pathogenic Variant

PURPOSE

Talazoparib has demonstrated efficacy in patients with BRCA-positive metastatic breast cancer. This study evaluated the pathologic response of talazoparib alone for 6 months in patients with a known germline BRCA pathogenic variant (gBRCA-positive) and operable breast cancer.

METHODS

Eligibility included 1 cm or larger invasive tumor and gBRCA-positive disease. Human epidermal growth factor receptor 2-positive tumors were excluded. Twenty patients underwent a pretreatment biopsy, 6 months of once per day oral talazoparib (1 mg), followed by definitive surgery. Patients received adjuvant therapy at physician's discretion. The primary end point was residual cancer burden (RCB). With 20 patients, the RCB-0 plus RCB-I response rate can be estimated with a 95% CI with half width less than 20%.

RESULTS

Twenty patients were enrolled from August 2016 to September 2017. Median age was 38 years (range, 23 to 58 years); 16 patients were gBRCA1 positive and 4 patients were gBRCA2 positive. Fifteen patients had triple-negative breast cancer (estrogen receptor/progesterone receptor < 10%), and five had hormone receptor-positive disease. Five patients had clinical stage I disease, 12 had stage II, and three had stage III, including one patient with inflammatory breast carcinoma and one with metaplastic chondrosarcomatous carcinoma. One patient chose to receive chemotherapy before surgery and was not included in RCB analyses. RCB-0 (pathologic complete response) rate was 53% and RCB-0/I was 63%. Eight patients (40%) had grade 3 anemia and required a transfusion, three patients had grade 3 neutropenia, and 1 patient had grade 4 thrombocytopenia. Common grade 1 or 2 toxicities were nausea, fatigue, neutropenia, alopecia, dizziness, and dyspnea. Toxicities were managed by dose reduction and transfusions. Nine patients required dose reduction.

CONCLUSION

Neoadjuvant single-agent oral talazoparib once per day for 6 months without chemotherapy produced substantial RCB-0 rate with manageable toxicity. The substantive pathologic response to single-agent talazoparib supports the larger, ongoing neoadjuvant trial (ClinicalTrials.gov identifier: NCT03499353).

Evaluation of predictive biomarkers for AR therapy and to identify the LAR subtype of TNBC

595

Background: Androgen-receptor-like (LAR) triple-negative breast cancer (TNBC) is a subtype identified using Vanderbilt’s molecular signature. LAR subtype has the lowest pCR rate for NACT among all TNBC subtypes (10% vs. 28% for TNBC in general). We launched a clinical trial to determine the effectiveness of enzalutamide and paclitaxel (ZT) in improving this poor chemo. response in the neoadjuvant setting for pts with anthracycline-refractory, androgen receptor (AR)+ TNBC (NCT02689427). However, we do not yet have a robust predictive biomarker to detect an activated AR pathway and have not seen a robust correlation between molecular LAR subtype and AR IHC staining intensity. Methods: Molecular profiling and immunohistochemical analysis of key biomarkers (LAR, Ki67, and vimentin) was performed for all pts enrolled in A Randomized triple negative breast cancer enrolling Trial to Confirm Molecular Profiling Improves Survival (ARTEMIS; NCT02276443). Patients receive 4 cycles of AC, followed by an experimental arm or standard taxane, tailored using nuclear IHC staining. IHC staining of ≥30% AR+ was used as a threshold for selection for enzalutamide combination arm. We evaluated the concordance between LAR-subtype using molecular profiling vs % AR+ cells via IHC. Results: As part of the clinical trial, tumors with ≥30% AR+ cells were classified as LAR. In addition, we used RNA profiling to assign Vanderbilt subtype scores, resulting in classification of 15 tumors as LAR+. We observed a significant correlation (r=0.75) between LAR score and %AR+ cells, with 13 of 15 LAR tumors having ≥30% AR+ cells. Among patients with high % of AR+ tumor cells, 11 received enzalutamide, with 43% (3/7) having responses (pCR or RCB-I). Conclusions: Comparison on numerical scores for Vanderbilt subtype and IHC scores suggests ≥30% AR+ IHC staining as the threshold (ppv=0.65, npv=0.98, Table) to identify the molecular LAR subtype. We observed a trend where response rate was higher in patients with ≥ AR+ IHC scores treated with enzalutamide; however, these results need confirmation in a larger cohort of patients. Clinical trial information: NCT02689427, NCT02276443. [Table: see text]

Beyond TILs: Predictors of pathologic complete response (pCR) in triple-negative breast cancer (TNBC) patients with moderate tumor-infiltrating lymphocytes (TIL) receiving neoadjuvant therapy

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Background: Increased TIL in TNBC is associated with higher rates of pCR. High TIL is also associated with improved disease free survival and overall survival. The aim of this study is to identify data cut-points of pre-treatment low, moderate and high TIL count based on pCR and to identify clinical and pathological predictors of pCR in patients with moderate TIL. Methods: We evaluated the relationship between pCR and TIL in 180 patients with stage I-III TNBC enrolled in the ARTEMIS trial (NCT02276443). Recursive portioning was used to identify cut-points. Clinical and pathological variables such as age at diagnosis, stage, race, histology as well as Ki-67, vimentin, and androgen receptor (AR) by immunohistochemistry, were evaluated in pts with moderate TIL. A multivariable logistic regression model identified variables independently, significantly associated with pCR. Results: Four TIL groups were identified with pCR rates of 23%, 31%, 48% and 78% respectively (p < 0.0001) (Table A). In the two combined moderate TIL groups, 90 (97%) pts were evaluable for the multivariate model. Stage I-II disease, high Ki-67 and low AR were associated with increased probability of pCR (Table B). The multivariable logistic regression model area under the ROC curve was 0.78 (95% CI=0.68-0.88; p<0.0001). A model of computed risk score [ Stage I-II (score 2)+Ki-67≥ 50% (score 1)+AR<10% (score 1)] predicted a probability of 67% for pCR when all three variables were favorable (Table). Conclusions: Four TIL groups were identified. In pts with moderate TIL levels, early stage disease, high Ki-67 and low AR were associated with increased probability of pCR with neoadjuvant therapy. [Table: see text]

CLO19-036: Folate Receptor alpha Expression in Metastatic Triple-Negative Breast Cancer (TNBC)

Background: Folate receptor alpha (FRα) is a glycosyl phosphatidylinositol (GPI)-anchored cell surface protein that binds and internalizes folate, which is a cofactor required for DNA/RNA synthesis and cell growth and proliferation. There is a marked up-regulation of FRα in many solid tumors; in contrast, FRα has a minimal expression in adult normal tissue. Mirvetuximab soravtansine is an antibody drug conjugate (ADC) consisting of a maytansinoid, N2'-Deacetyl-N2'-(4-mercapto-4-methyl-1-oxopentyl)-maytansine (DM4), conjugated to an anti-FRα antibody, M9346A. Once bound to the FRα and internalized, the anti-mitotic agents are released and inhibit tubulin polymerization and microtubule assembly, leading to cell death. Here we report the expression of FRα+ on residual tumor samples in metastatic TNBC. Methods: 68 patients (Pts) with stage IV TNBC underwent prescreening to determine if residual tumor tissue expressed FRα. Formalin fixed paraffin embedded (FFPE) samples were sent to Ventana Translational Diagnostics CAP/CLIA Laboratory for analysis using an in-house developed assay, Ventana OptiView DAB Detection kit, and the Ventana BenchMark Ultra automated slide stainer. FRα expression was evaluated by board certified pathologists using a scoring scale 1+ (low), 2+ (medium), and 3+ (high). For the purposes of study entry, FRα expression on cell surface was required to be low, defined as >25% of cells having 1+ expression. Results: 12% (8/68) of evaluated TNBCs had moderate to high rates of FRα expression. The median age of pts screened for FRα was 53 years. Moderate to high FRα expression rates were more common in Black and Asian patients (Table 1). Conclusion: Our prospective study has demonstrated that moderate to high expression of FRα in metastatic TNBC is 12%, which is lower than previously reported. An ongoing phase II study will determine efficacy for mirvetuximab soravtansine in advanced TNBC. Acknowledgement: This study was approved and funded in part by the NCCN Oncology Research Program from general research support provided by ImmunoGen, Inc.

Abstract OT1-03-04: INTERACT- INTegrated Evaluation of Resistance and Actionability using Circulating Tumor DNA in hormone receptor (HR) positive metastatic breast cancers (MBC)

Background

Mutations in the ligand-binding domain of ESR1 have been demonstrated to mediate resistance to aromatase inhibitors (AI) and are associated with poor survival. Analyses of circulating tumor DNA (ctDNA) offer a minimally invasive and real-time approach to characterize genomic landscape, clonal evolution, and treatment response. Early detection and intervention with alternate therapy to overcome resistance at minimal disease burden progression could have a larger impact than treating higher burden disease at clinical progression. However, whether treatment decisions made based on the emergence of secondary resistance mutations or mutant allele fraction (MAF) changes in ctDNA can improve clinical outcomes is unknown. Currently, the most effective therapy for patients harboring ESR1 mutations is unclear; although, pre-clinical and retrospective clinical trial analyses have suggested that some of these mutations may exhibit greater sensitivity to fulvestrant, a selective estrogen receptor down-regulator, compared to AI. This study hypothesizes that real-time monitoring of ctDNA for secondary ESR1 alterations can identify subclinical progression and early intervention with a targeted-agent that has greater efficacy against ESR1 mutations can improve disease-free survival.

Trial Design

This is a randomized, open-label, Phase-2 study for HR-positive MBC patients who are on AI and CDK 4/6 inhibitor as first line therapy. Patients on treatment for at least 12 months without evidence of clinical progression would be screened for ESR1 mutations using Guardant360 ctDNA assay. Patients with positive ESR1 mutations would be randomized to change of endocrine therapy to fulvestrant vs. continuing AI.

Eligibility criteria

-Histologically confirmed HR-positive (ER and/or PR &gt;10%) and HER2-negative MBC

-On AI with CDK4/6 inhibitor as first line therapy for 12 months without evidence of clinical progression

-Activating ESR1 mutation identified on ctDNA

-ECOG performance status ≤1

-Normal organ and marrow function

Specific aims

- To assess progression-free survival (PFS) with transition to fulvestrant compared with continuing AI therapy in patients with emergence of ESR1 mutations in plasma

-To assess ctDNA ESR1 mutant allele fraction and kinetics with transition to fulvestrant compared with AI

-To assess the prevalence of ESR1 mutations in patients with exposure to endocrine therapy

-To assess overall survival with fulvestrant transition compared with continuing AI therapy in patients with emergence of ESR1 mutations

Statistical methods

To detect a change in median PFS from 5 months (for AI arm) to 9 months (with fulvestrant arm) would require about 124 patients (5% two-sided alpha, 80% power, log rank testing). Interim analysis will be performed when 42 PFS events are observed. Using O'Brien-Fleming stopping boundaries, we will stop for futility if the log rank test p-value &gt; 0.72 and stop for success if it is &lt; 0.004.

Citation Format: Damodaran S, Meric-Bernstam F, Hess KR, Litton JK, Raymond V, Lanman R, Ueno NT, Hamilton S, Wistuba II, Valero V, Moulder SL, Tripathy D. INTERACT- INTegrated Evaluation of Resistance and Actionability using Circulating Tumor DNA in hormone receptor (HR) positive metastatic breast cancers (MBC) [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr OT1-03-04.

Abstract P1-18-04: CTCs and SUV to predict the efficacy of the bone-specific radiopharmaceutical agent radium-223 dichloride combined with hormonal therapy for hormone receptor-positive bone-dominant breast cancer metastasis

Background: Radium-223 dichloride (Ra-223) is a targeted alpha particle-based radiotherapeutic that has a localized cytotoxic effect on bone metastases. We sought to determine whether the circulating tumor cell (CTC) count and the presence of CTCs in epithelial-mesenchymal transition (EMT-CTCs) along with the standardized uptake value (SUV) on positron emission tomography-computed tomography (PET/CT) scans predict the efficacy of combined Ra-223 and hormonal therapy in patients with hormone receptor (HR)-positive bone-dominant metastatic breast cancer.

Patients and Methods: In this single-center phase 2 study (NCT02366130), 36 patients received Ra-223 (55 kBq/kg intravenously) on day 1 and then every 4 weeks for six cycles. Patients also received a standard care endocrine monotherapy. One non-bone metastatic site was allowed. The number of prior endocrine therapies was not limited and one prior chemotherapy was allowed for metastasis. Response was evaluated using the PET Response Criteria in Solid Tumors (PERCIST) with PET/CT at baseline, 6 and 9 months (mo) later. The CTC count (CellSearch) and the presence of EMT-CTCs (AdnaTest) was determined at baseline, 6 and 9 mo later. Progression-free survival (PFS) time was calculated to evaluate efficacy.

Results: Seven patients (20%) had a non-bone metastatic site. The median number of prior therapies for metastasis was 1 (range, 0-4). Six patients (17%) received chemotherapy. The median CTC count at baseline was 4 (range, 0-306). Only four patients (11%) were positive for EMT-CTCs at baseline. The median follow-up time was 14.7 mo (95% confidence interval [CI], 13.2 mo-not reached [NR]). The disease control rate at 9 mo was 46% in 33 patients who reached 9 mo or progressed up to 9 mo. The tumor response rate at 6 mo was 52% (complete/partialresponse rate; 22/30 %) in 27 patients whose disease was evaluable using PERCIST. The SUV on PET/CT decreased significantly at 6 and 9 mo after baseline (average decreases of 1.5 (p=0.0004) and 2.5 (p=0.0054), respectively). The median PFS duration was 7.4 mo (95% CI, 4.8 mo-NR). The median bone PFS was 16 mo (95% CI, 7.3 mo-NR). Patients with bone-only metastasis (N=28, 80%) had a significantly longer median PFS duration than did patients with non-bone metastases at baseline (N=7, 20%) (13.8 mo versus 4.5 mo; p=0.017). Patients without prior treatment (N=12, 34%) tended to have longer median PFS durations than did those who underwent prior treatment (N=23, 66%) (16.8 mo versus 4.8 mo; p=0.1865). Also, patients with &lt;5 CTCs at baseline (N=19, 54%) tended to have longer median PFS durations than did those with ≥5 CTCs (N=16, 46%) (13.8 mo versus 4.8 mo; p=0.1277). EMT-CTCs status did not predict efficacy.

Conclusions: Bone-only metastatic breast cancer and SUV suppression by Ra-223 are predictive of efficacy. Patients with baseline &lt;5 CTC count tended to have better outcomes than did those with ≥5 CTCs. Combined treatment with Ra-223 and a hormonal agent is especially effective at controlling bone metastasis in patients with HR-positive breast cancer. Bone-only metastatic disease and CTC count should be factored in future clinical trial designs.

Citation Format: Ueno NT, Tahara RK, Reuben JM, Gao H, Saigal B, Fujii T, Lucci A, Ibrahim NK, Damodaran S, Shen Y, Liu DD, Hortobagyi GN, Tripathy D, Lim B, Chasen BA. CTCs and SUV to predict the efficacy of the bone-specific radiopharmaceutical agent radium-223 dichloride combined with hormonal therapy for hormone receptor-positive bone-dominant breast cancer metastasis [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P1-18-04.