Regorafenib plus nivolumab in patients with mismatch repair-proficient/microsatellite stable metastatic colorectal cancer: a single-arm, open-label, multicentre phase 2 study

Background

Anti-programmed cell death protein 1 antibodies plus multikinase inhibitors have shown encouraging activity in several tumour types, including colorectal cancer. This study assessed regorafenib plus nivolumab in patients with microsatellite stable/mismatch repair-proficient metastatic colorectal cancer.

Methods

This single-arm, open-label, multicentre phase 2 study enrolled adults from 13 sites in the USA with previously treated advanced microsatellite stable/mismatch repair-proficient metastatic colorectal cancer. Eligible patients had known extended RAS and BRAF status, progression or intolerance to no more than two (for extended RAS mutant) or three (for extended RAS wild type) lines of systemic chemotherapy and an Eastern Cooperative Oncology Group performance status of 0 or 1. Regorafenib 80 mg/day was administered orally for 3 weeks on/1 week off (increased to 120 mg/day if 80 mg/day was well tolerated) with intravenous nivolumab 480 mg every 4 weeks. Primary endpoint was objective response rate. Secondary endpoints included safety, overall survival, and progression-free survival. Exploratory endpoints included biomarkers associated with antitumour activity. Patients who received at least one dose of study intervention were included in the efficacy and safety analyses. Tumour assessments were carried out every 8 weeks for the first year, and every 12 weeks thereafter until progressive disease/end of the study, and objective response rate was analysed after all patients had met the criteria for primary completion of five post-baseline scans and either 10-months' follow-up or drop out. This trial is registered with ClinicalTrials.gov, number NCT04126733.

Findings

Between 14 October 2019 and 14 January 2020, 94 patients were enrolled, 70 received treatment. Five patients had a partial response, yielding an objective response rate of 7% (95% CI 2.4-15.9; p = 0.27). All responders had no liver metastases at baseline. Median overall survival (data immature) and progression-free survival were 11.9 months (95% CI 7.0-not evaluable) and 1.8 months (95% CI 1.8-2.4), respectively. Most patients (97%, 68/70) experienced a treatment-related adverse event; 51% were grade 1 or 2, 40% were grade 3, 3% were grade 4, and 3% were grade 5. The most common (≥20%) events were fatigue (26/70), palmar-plantar erythrodysesthesia syndrome (19/70), maculopapular rash (17/70), increased blood bilirubin (14/70), and decreased appetite (14/70). Higher baseline expression of tumour biomarkers of immune sensitivity correlated with antitumour activity.

Interpretation

Further studies are warranted to identify subgroups of patients with clinical characteristics or biomarkers that would benefit most from treatment with regorafenib plus nivolumab.

Funding

Bayer/Bristol Myers Squibb.

MOUNTAINEER-03: Phase 3 study of tucatinib, trastuzumab, and mFOLFOX6 as first-line treatment in HER2+ metastatic colorectal cancer—Trial in progress

TPS261

Background: Current standard of care (SOC) for treatment (tx) of metastatic colorectal cancer (mCRC) is multi-agent chemotherapy, w/ or w/o a VEGF- or EGFR-inhibitor. HER2 is a validated clinical target in breast and gastric cancers. HER2 amplification occurs in 3%-5% of patients (pts) w/ mCRC; the rate of HER2 amplification can increase to ~10% in pts w/ RAS/BRAF wild-type mCRC tumors. Tucatinib (TUC), a highly selective, HER2-directed tyrosine kinase inhibitor, is approved in multiple regions for HER2+ metastatic breast cancer and is being investigated in gastrointestinal cancers. MOUNTAINEER (NCT03043313) evaluated the safety and efficacy of TUC and trastuzumab (Tras) in pts w/ tx refractory RAS wild-type, HER2+ mCRC. Results from the primary endpoint analysis showed clinically meaningful activity (confirmed ORR of 38.1% and median DOR of 12.4 months) and demonstrated TUC + Tras was well tolerated with a low discontinuation rate (5.8%) and no deaths due to AEs. MOUNTAINEER-03 will further investigate TUC in combo w/ mFOLFOX and Tras in pts w/ RAS wild-type, HER2+ mCRC. Methods: MOUNTAINEER-03 (NCT05253651) is a global, open label, randomized, phase 3 study for 1L tx of HER2+ and RAS wild-type mCRC. Approximately 400 pts will be randomized 1:1 to the TUC experimental arm (TUC [300 mg PO BID] + Tras + mFOLFOX) or the SOC arm (mFOLFOX alone or in combo w/ either bevacizumab or cetuximab). HER2 status is determined centrally w/ tissue based HER2 immunohistochemistry and in situ hybridization assays. Eligible pts must not have received prior tx in the metastatic setting but may have received adjuvant tx if completed > 6 months prior to enrollment. Pts must be ≥18 years of age w/ an ECOG performance status of ≤1 and RAS wild-type mCRC. Pts w/ treated stable central nervous system metastases are eligible. Randomization is stratified by primary tumor location (left-sided vs other) and liver metastases (presence/absence). Primary endpoint is progression-free survival per RECIST v1.1, assessed by blinded independent central review (BICR). Key secondary endpoints are overall survival and confirmed objective response rate per RECIST v1.1 assessed by BICR. Enrollment is ongoing in the US, w/ global sites planned. Clinical trial information: NCT05253651 .

Utility of circulating tumor DNA (ctDNA) in the management of appendiceal adenocarcinoma (AA)

226

Background: Appendiceal adenocarcinoma (AA) is a rare and heterogenous cancer with marked differences in clinical course between high- and low-grade tumors. Unlike colorectal cancer (CRC) and other gastrointestinal malignancies, AA virtually never has hematogenous metastases, rather, metastasis is limited to the peritoneum. Here we present a retrospective, single institution study of AA to identify the prevalence of detectable ctDNA, evaluate the clinical predictive value of positive ctDNA, and assess what clinical, pathologic, or molecular features predict positive ctDNA. Methods: 160 blood samples from 147 patients with AA metastatic to the peritoneum were profiled with a CLIA approved 73 gene mutational panel as part of routine clinical practice. Paired tumor sequencing was available for 73 patients. Survival was measured starting from day ctDNA was drawn. Mutations that most likely represented clonal hematopoiesis were removed from analysis. Results: Out of 160 ctDNA samples, 120 were taken in the setting of radiographically apparent metastatic disease. Of these, 46 (38.3%) had any detectable mutation. 40 ctDNA tests were performed when patients had no radiographic evidence of disease (NED); 15 (37.5%) of which had any detectable mutation. High-grade tumors were more likely to have detectable ctDNA with detection rates of 10/46 (21.7%), 18/46 (39.1%), and 33/68 (48.5%) for well, moderately, and poorly-differentiated tumors, respectively. Restricting analysis to the 73 patients with paired tissue and blood samples and 73 genes sequenced in both, of 81 mutations detected in tumor only, 21 were detected in blood (sensitivity of 26%). Sensitivity was highest for mutation in TP53 (53.8%) suggesting these tumors may have a greater propensity to shed DNA into circulation. Overall, the sensitivity of ctDNA detection in metastatic AA was markedly less than what was observed in a cohort of 274 metastatic CRC patients from the same institution (288/581 = 49.6%). For AA patients with detectable ctDNA, variant allele frequency (VAF) in AA was significantly lower compared to CRC (median VAF 0.04% vs. 6%, p = <0.0001). Detectable ctDNA was associated with shorter overall survival (46.2 mo for positive ctDNA vs. not-yet-reached for negative ctDNA, HR = 2.5, p = 0.016) and shorter disease free survival (DFS) (60 mo vs. not-yet-reached, HR = 3.4, p = 0.05). As expected, patients with radiographic evidence of disease did worse than patients with NED (HR = 2.1. p = 0.08), but of note this hazard ratio was less than that for positive ctDNA. Conclusions: In patients with AA, the presence of detectable ctDNA is associated with shorter overall and disease-free survival. Sensitivity of ctDNA detection in metastatic AA is overall markedly lower than CRC, with detection more likely in high-grade tumors and higher sensitivity in tumors containing TP53 mutation.

Utility of tumor marker levels in predicting survival of patients with appendiceal adenocarcinoma

221

Background: Due to the rarity of appendiceal adenocarcinomas (AA), systematic study of these tumors has been limited. Thus, guidelines for the diagnosis and treatment of AA are often based on other related tumor types such as colorectal cancer. However, given that AA has been shown to be molecularly and functionally distinct, there is a need for focused clinical data to guide disease management. In AA, tumor marker levels are used by some practitioners to monitor response to treatment and aid in diagnosis. This study evaluates the association of elevated tumor marker levels with survival outcomes. Methods: The MDACC database was queried to identify patients with AA between 1997 to 2022. Patients with reported values for the tumor markers CA-125 (n=1076), CA 19-9 (n=1060), and CEA (n=1249) were then selected for analysis. Elevation of tumor markers was defined as above the laboratory upper limit of normal (CA-125 > 37 U/mL, CA 19-9 > 37 U/mL, and CEA > 3 ng/mL and survival outcomes were compared with a log-rank (Mantel-Cox) test. This analysis was repeated while controlling for tumor grade, which was defined by low-grade: well, well to moderately differentiated and high-grade: moderate, moderate to poor, and poorly differentiated. Results: Elevated CA-125 was predictive of overall survival in all patients with median survival not-yet-reached for those with normal CA-125 vs. 87.4 months for those with elevated CA-125 (HR: 5.8, p < 0.0001). Similarly, elevated CA 19-9 and CEA were also predictive of overall survival (HR: 2.8, 4.6, respectively, p < 0.0001 for each). Given that tumor grade is the primary driver of prognosis in AA, survival analysis was repeated while controlling for tumor grade. While elevated levels of all tumor markers were predictive of overall survival for both low-grade and high-grade tumors, elevated CA-125 was an especially strong predictor of survival in patients with high-grade tumors (OS: 69.8 months vs. not-yet-reached, HR: 14.3, p < 0.0001). Moreover, high-grade patients with elevated CA-125 had a reduced 5-year survival rate of 56% vs. 91%. Elevated CA-125 also stratified 5-year survival rate in low-grade patients (83% vs. 99%). Elevated levels of CA 19-9 and CEA were strongly predictive of overall survival for patients with low-grade tumors (HR: 10.6, 26.8, respectively, p < 0.0001 for each). Notably, patients with low-grade tumors expressing normal levels of CA 19-9 or CEA had excellent 5-year survival rates of 99% and 100%, respectively. Conclusions: These results highlight the utility of using tumor marker levels in conjunction with tumor grade to more accurately predict prognosis in AA. CA 19-9 and CEA were particularly useful indicators of outcome in patients with low-grade AA, while CA-125 had greatest prognostic value in high-grade tumors.

A randomized phase 2 study of trastuzumab and pertuzumab (TP) compared to cetuximab and irinotecan (CETIRI) in advanced/metastatic colorectal cancer (mCRC) with HER2 amplification: SWOG S1613

140

Background: HER2 ( ERBB2) over-expression and amplification (HER2+) is seen in a small but distinct subset (2-3%) of mCRC and is enriched in RAS/BRAF wild type (WT) tumors. This subset is characterized by a limited response to anti-epidermal growth factor receptor monoclonal antibody-based (anti-EGFR) therapy and a promising response to dual-HER2 inhibition. Methods: In this multicenter, open label, randomized, phase 2 trial, we enrolled 54 patients with RAS/BRAF WT HER2+ mCRC who had had disease progression after 1 or 2 previous therapies. HER2 status was confirmed centrally with immunohistochemistry (IHC) and in-situ hybridization (ISH). HER2+ was defined as IHC 3+ or 2+ and ISH amplified (dual-probe HER2/CEP17 ratio > 2.0). Patients were then randomly assigned in a 1:1 ratio to receive either TP (trastuzumab [loading 8 mg/kg then 6 mg/kg] + pertuzumab [loading 840 mg then 420 mg] every 3 weeks) or CETIRI (cetuximab 500 mg/m2 + irinotecan 180 mg/m2 every 2 weeks). Crossover was allowed for patients on CETIRI arm to TP (cTP) after progression. Restaging (per RECIST v1.1) was performed at 6 and 12 weeks and then every 8 weeks until progression. The primary endpoint was progression-free survival (PFS). Key secondary endpoints were overall response rate (ORR), overall survival (OS) and safety. Results: A total of 54 (out of planned 62 due to low accrual) patients were randomized to TP (26) and CETIRI (28) between 10/2017 and 12/2021. By 8/18/2022, 20 patients had crossed over to cTP arm. One CETIRI patient was not analyzable. The results for key endpoints by protocol defined stratification factors, prior irinotecan (Piri) (yes or no) and HER2/CEP17 ratio (HCR) (>5 or ≤5), are summarized as of data cut-off of 9/6/2022. PFS did not vary significantly by treatment: medians 4.4 (95%CI: 1.9 – 7.6) months in TP group and 3.7 (95%CI: 1.6 – 6.7) months in CETIRI group (p = 0.35). Grade ≥3 adverse events occurred in 23%, 46% and 40% of patients in TP, CETIRI and cTP groups. Conclusions: Dual-HER2 inhibition with TP appears to be a safe and effective treatment option for patients with RAS/BRAF WT HER2+ mCRC with a promising response rate of 31%. Higher level of HER2 amplification may provide a greater degree of clinical benefit from TP compared to CETIRI. Future correlative efforts will explore biomarkers of response/resistance with this strategy. Clinical trial information: NCT03365882 . [Table: see text]

A prospective randomized crossover trial of systemic chemotherapy in patients with low-grade mucinous appendiceal adenocarcinoma

163

Background: Appendiceal adenocarcinoma is both a rare and heterogenous tumor, with marked contrast in the natural history of low-grade and high-grade tumors (5-year OS 68% for low-grade vs. 7% for high-grade). While low-grade appendiceal adenocarcinoma is primarily treated with surgical resection sometimes followed by hyperthermic intraperitoneal chemotherapy (HIPEC), many inoperable candidates are treated with systemic chemotherapy although there is no prospective data supporting this practice. The purpose of our study was to objectively evaluate the effectiveness of systemic chemotherapy in low-grade mucinous appendiceal adenocarcinoma. Methods: A randomized crossover trial of surgically unresectable low-grade (well differentiated) mucinous appendiceal adenocarcinoma was performed with patients randomized to either 6 months observation followed by 6 months of chemotherapy (physician’s choice), or initial chemotherapy followed by observation. In this way each patient would serve as their own control. Enrollment of 30 patients was planned to have complete 6- and 12-month tumor measurements for 24 patients, providing 80% power at 0.05 significance level to detect a 5.0% difference in change in tumor size as measured by peritoneal RECIST in observation vs. treatment periods. Results: The trial closed early due to slow accrual. A total of 24 patients were enrolled. The majority of patients were treated with either 5FU or capecitabine (n = 15, 63%), bevacizumab was added for 3 (13%), and 3 were treated with doublet chemotherapy (FOLFOX/FOLFIRI). 15 patients who completed both treatment and observation periods were available for the primary analysis, the mean difference in tumor size was -4.5% (95% CI: -12.6, 3.7), indicating a slight trend towards faster growth on treatment than observation. This difference was not statistically or clinically significant (8.4% growth on treatment vs. 4.0% observation, p=0.26). Of the 18 patients who received any chemotherapy during the study period, zero achieved an objective response, 14 (77.8%) had stable disease during the entire year of follow up, and 4 (12.2%) had progression on study. Patient reported quality of life metrics identified that fatigue (p=0.02), peripheral neuropathy (p=0.014), and financial difficulty (p=0.0013) were all significantly worse while on treatment. There was not a significant difference in rate of bowel obstruction between the treatment first vs. observation first arms (12.5%, (n=3) vs 8.3%, (n=2)). Conclusions: These data from a prospective, randomized crossover trial indicate that patients with low-grade mucinous appendiceal adenocarcinoma do not derive benefit from 5FU based chemotherapy but do incur toxicity. These data further highlight the unique biology of low-grade appendiceal cancer and demonstrates the need to identify novel systemic therapies for this patient population. Clinical trial information: NCT01946854 .

ctDNA-based fusion detection for advanced colorectal cancer with a partner-agnostic assay

186

Background: Actionable mutations can predict therapeutic benefit in patients with advanced malignancies, though clinical relevance of fusion testing for advanced colorectal cancer (aCRC) remains undefined. Identification of fusions from circulating tumor DNA (ctDNA) has previously been restricted to defined oncogenic fusion partners. To improve the sensitivity for fusion detection, we evaluated a partner-agnostic fusion analysis from ctDNA of patients with aCRC. Methods: De-identified data from Guardant Health was reviewed for 18,558 patients with aCRC who underwent ctDNA NGS testing by Guardant360 (Redwood City, CA) between 2017-2022. Fusion results were analyzed with a partner-agnostic bioinformatic approach. A fusion was defined as “clonal” if the variant allele frequency (VAF) ratio exceed ≥50% of highest somatic VAF, and “subclonal” if < 50% maxVAF. Microsatellite instability (MSI) status [MSI-high (bMSI-H) or microsatellite stable (bMSS)] and anti-EGFR exposure signature were determined using prior methods. Associations between fusion occurrence and coexisting alterations were performed using Fisher’s exact test. Results: Fusions were detected in 221 (1.2%) of patients with aCRC. 258 activating fusions were detected in 187 patients; FGFR3 (N = 59, 23%), RET N = 55, 21%), BRAF (N = 43, 17%), and ALK (N = 41, 16%) were most frequent. There were 71 previously unreported fusions in 28 additional patients; RET (N = 16; 23%), MET (N = 15, 21%), and BRAF (N = 11; 15%) were most prevalent. Clonal fusions occurred in 7% (18/258) of all activating fusions; RET (5/18, 28%) and FGFR3 (3/18, 17%) were most common and associated with bMSI-H status relative to bMSS (27% vs 4%, OR 8.165, 95% CI 2.332-33.99; p = 0.0076). Clonal fusions occurred less commonly in samples with a prior EGFR signature (OR 0.22, 95% CI 0.05-0.997, p = 0.049). Most detected fusions were subclonal including ALK, FGFR1-3, MET, RET and ROS1. Conclusions: Highly specific partner-agnostic fusion detection is feasible to increase sensitivity of ctDNA assay performance. Oncogenic fusions occurred in ~1% of all patients with aCRC. Clonal fusions as oncogenic drivers were infrequent and associated with bMSI-H status. Subclonal fusions were more common and occur in a setting consistent with prior exposure to anti-EGFR therapies. Reporting fusion partners and clonality from ctDNA may guide oncologists on the appropriate context for consideration of fusion-directed treatments.

Goblet cell tumors of the appendix: Clinical and molecular features

223

Background: Goblet Cell tumors (GCTs) of the appendix are a rare, distinct, and under studied malignancy. Since 2019 the preferred World Health Organization (WHO) terminology is Goblet Cell Adenocarcinoma (GCA), but previously many terms have been used to describe these tumors including Goblet Cell Carcinoid and Adenocarcinoma ex goblet cell carcinoid as these tumors have a histological appearance that blends neuroendocrine and adenocarcinoma features. Historically goblet cell tumors have been considered one of the more aggressive subtypes of appendiceal cancer, but limited data exists and is mostly in the form of case reports. Here we present the retrospective analysis of a large single institution cohort. Methods: The internal database of the University of Texas MD Anderson Cancer Center (MDACC) was queried to identify all patients diagnosed with goblet cell appendiceal tumor. Patients were classified to two different histopathological groups, GCA (n=220) and GCA with signet ring adenocarcinoma (SRA) (n=146). Clinical, histopathological, and molecular data were extracted from the database in semi-automated fashion. Survival analysis were performed using Kaplan Meier methodology. Results: 366 patients with GCTs were identified from 1986 to 2022. 132 (36%) patients were seen during the last five years, with an average of 26 patients per year. Median follow up time was 54 months, while median age at diagnosis was 57 years. Tumor grade data was available for 294 patients. 95% of the patients had high grade tumors (moderately, moderately to poorly and poorly-differentiated) (n= 278), and 5% had low grade tumors (well and well to moderately-differentiated (n=16). The median overall survival was 85 months, and significantly different between the two groups, 118 months for the GCA group and 57 months for the GCA with SRA (p= 0.003). Lymph node (LN) status was known for 168 patients, rate of LN involvement was 53% (n=89) and significantly different between the two groups with 41% (n=39) for GCA and 68% (n=50) for GCA with SRA (p= <0.0006). The internal database of MDACC was queried for LN status of Mucinous adenocarcinoma (MA) (n=242) and SRA (n=104) for comparison purposes, rate of LN positivity was 13% in MA and 76% in SRA. Node positive patients had significantly worse overall survival with median overall survival of 51 months vs 85 months for node negative patients (p<0.004). By multivariate analysis, both LN status and SRA component were independent predictors of overall survival. 107 patients had gene mutation analysis tested, TP53, SMAD4, GNAS and KRAS were the most commonly mutated with 13%, 9%, 4%, and 3% respectively. Conclusions: This study highlights the heterogenicity of GCTs of the appendix and the importance of the histopathological classification in this distinct entity. GCT are much more likely to spread to LN and have a distinct somatic mutation profile relative to MA.

Phase 2 study of anti-EGFR rechallenge therapy with panitumumab with or without trametinib in advanced colorectal cancer

3520

Background: In RAS/RAF WT colorectal cancer (CRC), rechallenge with anti-EGFR therapy (EGFRi) in patients (pts) with prior response leads to clinical benefit, with response rates up to 30% in prior trials. However, secondary MTs in the MAPK signaling pathway have been implicated in resistance to EGFRi. We designed a phase 2 trial to evaluate the efficacy of EGFRi rechallenge +/- a MEK inhibitor (trametinib) based on pre-treatment ctDNA MTs. Methods: This trial evaluated the efficacy and safety of EGFRi rechallenge +/- trametinib in pts with RAS/BRAF WT, MSS, treatment refractory mCRC who achieved clinical benefit with prior EGFRi based therapy for ≥16 weeks with subsequent progression. Pre study ctDNA was used to enroll in one of 3 arms: Arm A: Pts with an acquired EGFR ECD MT but absence of RAS/BRAF/MAP2K1 or with absence of any acquired resistance MT (Arm C) at time of study initiation received panitumumab 6 mg/kg IV Q2 wks. Arm B: Pts with an acquired RAS/BRAF/MAP2K1 MT received panitumumab 4.8 mg/kg plus trametinib 1.5 mg PO daily. Pts in Arms A and C were allowed to cross over on progression. The primary endpoint was ORR by RECIST v1.1. Results: 54 pts were enrolled, with 52 evaluable for efficacy. Median age is 59 yrs (range, 37-78), and 23 (46%) are female. Median number of prior therapies was 3. Three, 20, and 31 pts were enrolled in Arms A, B, C, respectively. Grade 3 TREAs occurred in 29 (54%) pts (all receiving the doublet regimen) and included acneiform rash in 17 (31%) and others occurring in < 5% of pts. There were no grade 4 TRAEs. In pts with no acquired MTs (Arm C), ORR was 20% (6/30) (95% CI, 0.07-0.37), DCR 67% (20/30) (95% CI, 0.45- 0.81), and median PFS and OS 4.1 mo and 11.2 mo, respectively. The median DOR was 5.5 mo. 22 patients crossed over to add trametinib at time of progression, without any responses. In contrast, in pts with acquired RAS/RAF/MAP2K1 MTs (Arm B), there were no responses, with DCR of 63% (12/19) (95% CI, 0.36-0.81), and median PFS and OS 2.1 mo and 5.9 mo, respectively. Only 3 pts were identified with EGFR ECD MTs (Arm A), and ORR is 0% (0/3) in this cohort, with DCR 67% (2/3) (95% CI, 0.09-0.99). Pts with PR had a longer median interval from prior EGFRi and longer time on prior EGFRi than those with SD+PD (5.5 vs 3.6 mo; p = 0.03, and 9.5 vs. 8.8 mo; p = 0.03, respectively). Conclusions: CtDNA guided rechallenge leads to responses in 20% of pts without acquired resistance MTs, with DCR of 67%. This exceeds current third line standard options. While panitumumab has the potential to block EGFR ECD mutations arising from cetuximab, these mutations in isolation were uncommon and there were no signals of efficacy. Although the acneiform rash induced by the combination of MEK and EGFR inhibition was manageable with close dermatologic management, the combination failed to improve outcomes for pts with acquired resistance. Alternative approaches to downstream MAPK blockade should be explored to improve outcomes. Clinical trial information: NCT03087071.

RAS co-mutation and early onset disease represent an aggressive phenotype of atypical (non-V600) BRAF mutant metastatic colorectal cancer

3592

Background: While BRAFV600E accounts for the majority of BRAF mutations in mCRC, non-V600 BRAF variants (a BRAF) have emerged in recent years as a distinct molecular subtype. There are no consensus recommendations regarding management. This study provides a comprehensive profile of a BRAF, their clonalities and co-mutations in mCRC using a large genomic database as well as a prospective treatment cohort of patients with a BRAF and mCRC managed at a single center. Methods: A systematic analysis was performed of patients with mCRC who underwent ctDNA testing (Guardant360 platform, Guardant Health) from September 2014 to May 2021. A variant was defined as clonal if the mutant allele frequency (MAF) was greater than 50% of the highest somatic MAF in the sample; otherwise it was defined as subclonal. Co-mutation analysis was conducted with BRAF, KRAS, NRAS, NF1, ERBB2, PIK3CA and SMAD4. Treatment history and overall survival (OS) for patients with a BRAF mCRC from MD Anderson Cancer Center were included. Results: 1,733 out of 14,742 mCRC patients had at least one BRAF variant, including 6.5% of patients with BRAFV600E variants and 6.2% with a BRAF variants (1.1% with class II, 1.9% with class III, and 3.2% with unclassified variants). 431 unique BRAF variants were identified in a total of 1,905 BRAF variants. BRAF class II and III variants showed a higher rate of co-occurring KRAS mutations (25.6% and 21.5%) and co-occurring NRAS mutations (5.8% and 2.7%) compared with BRAFV600E variants (2.4% for KRAS and 0.1% for NRAS); however, co-occurring KRAS G12C was only noted in one patient. In our MDACC cohort, 38 patients were included in the analysis. The median age was 55, 81% were Caucasian, and 74 % had left sided primary tumors (45% rectal, 24% sigmoid) with 37% being exposed to at least 2 lines of therapy. The most common mutations in clinical practice were class III, D594G (39%), followed by class II G469A (10%), & class III G466E (7%). The median follow-up time was 23.8 months (mo). While there were no survival differences between a BRAF classes II and III, there was a significant difference in OS in patients with RAS co-mutation (28.3 mo vs not reached [NR], p = 0.05) or liver involvement (28.8 mo vs NR, p = 0.02). Patients < 50 years of age had extremely poor survival with OS of 16.3 mo (vs. NR) and HR 7.51 (95% CI 1.82-31.0, p = 0.005). Treatment with anti-EGFR or use of metastasectomy was not associated with improved survival. Conclusions: a BRAF mutations have historically been considered a favorable prognostic marker in mCRC. Co-mutation with RAS is frequent for both classes and portends poor survival in our real-world cohort. Furthermore, early onset a BRAF mCRC is associated with more aggressive disease. These factors highlight the need for dedicated clinical trials for this unique subset of mCRC and may represent an opportunity to improve management in early onset colorectal cancer.

First-in-human, phase I study of TT-00420, a multiple kinase inhibitor, as a single agent in advanced solid tumors

3013

Background: TT-00420 is a spectrum-selective multi-kinase inhibitor that targets cell proliferation, angiogenesis, and immune-oncology pathways by inhibiting Aurora kinases A/B and Janus kinases (JAK) involved in cytokine signaling and receptor tyrosine kinases (FGFRs and VEGFRs) involved in the tumor microenvironment. TT-00420 has demonstrated anti-tumor activity in both in vitro and in vivo preclinical models of solid tumors, including triple-negative breast cancer (TNBC) and cholangiocarcinoma (CCA). Methods: This phase I, first-in-human, dose escalation and expansion study of TT-00420 ( NCT03654547 ) enrolled adult patients with advanced or metastatic solid tumors. Capsules in 1 mg or 5 mg formulation were administered orally once daily in 28-day cycles. Dose escalation was guided by Bayesian modeling with overdose control. The primary safety endpoints were to determine dose limiting toxicities (DLTs) and a dose recommended for dose expansion (DRDE). Secondary endpoints included pharmacokinetics (PK) and preliminary efficacy evaluated per RECIST v1.1 criterion. Results: As of February 7, 2022, 48 advanced solid tumor patients were enrolled in the study, and received at least one dose of TT-00420 in 7 dose levels: 1 mg q.d. (N = 1), 3 mg q.d. (N = 1), 5 mg q.d. (N = 4), 8 mg q.d. (N = 10), 10 mg q.d. (N = 6), 12 mg q.d. (N = 20), and 15 mg q.d. (N = 6). DLTs were observed in 3 out of 40 DLT-evaluable patients, including 1 patient at 8 mg q.d. who had Grade (Gr) 3 palmar-plantar erythrodysaesthesia syndrome and 2 patients at 15 mg q.d. who both had Gr 3 hypertension. Among the twenty (20) safety evaluable patients treated at 12 mg, the DRDE, drug-related TEAEs included hypertension (n = 11, 55.0%; Gr 3: n = 6, 30%); diarrhea (n = 7, 35%, Gr 3: n = 1, 5%); mucosal inflammation (n = 7, 35%; Gr 3: n = 1, 5%); palmar-plantar erythrodysaesthesia syndrome (n = 6, 30%; Gr 3: n = 0, 0%); and vomiting (n = 4, 20%; Gr 3: n = 0, 0%). No grade 4 suspected adverse events were reported. Out of 42 patients who had at least one post-baseline scan, 7 (16.7%) had a best response of partial response (PR) and 22 (52.4%) had stable disease (SD). Among 7 PRs, 3 were CCA patients (one for each treated at 8 mg, 10 mg, or 12 mg), 2 were TNBC patients (one for each at 10 mg, or 12 mg), 1 was HER2-negative BC patient at 12 mg, and 1 was CRPC patient at 12 mg. Sustainable stable disease for six months or longer was observed in patients with colon cancer (n = 1), head and neck cancer (n = 1), and peritoneal mesothelioma (n = 1). Conclusions: TT-00420 monotherapy was well tolerated and had favorable PK characteristics. The TEAEs observed in dose escalation and dose expansion cohorts were manageable with concomitant treatment and/or dose interruptions of TT-00420 and reversible upon the discontinuation of TT-00420 treatment. Taking safety, efficacy and clinical PK into consideration, 10 mg p.o. q.d. was recommended for phase II study of TT-00420 in patients with advanced CCA. Clinical trial information: NCT03654547.

Phase I/II trial of encorafenib, cetuximab, and nivolumab in patients with microsatellite stable (MSS), BRAFV600E metastatic colorectal cancer

3598

Background: Treatment with encorafenib (E) and cetuximab (C) offers response and survival benefit for patients (pts) with MSS, BRAFV600E metastatic colorectal cancer (CRC). BRAF + EGFR inhibition induced a transient MSI-H phenotype in preclinical models of MSS, BRAFV600E CRC and may prime these tumors for response to immunotherapy with anti-PD-1 antibodies like nivolumab (N). Methods: In this single-arm, single-institution, phase I/II clinical trial, pts with treatment-refractory MSS, BRAFV600E metastatic CRC were eligible. No prior BRAF, MEK, or ERK inhibitors, anti-EGFR antibody, or immunotherapy was permitted. Pts received E (300 mg PO daily), C (500 mg/m2 IV q14 days), and N (480 mg IV q28 days). The primary endpoints were best overall response (RECIST 1.1) and safety/tolerability (CTCAE v5). A Simon two-stage design (H0: p≤.22; Ha: p≥.45, where p = percentage of pts with radiographic response) was employed using a one-sided α =.05 and β =.20. Median progression-free survival (PFS) and overall survival (OS) were estimated via Kaplan-Meier. To measure ex vivo treatment responses with an E-slice assay (EMPIRI), 300 µm fresh tissue slices from core biopsies were generated and cultured in serum-free media with E, C, and N. Longitudinal changes in viability were measured at days 4, 8, and 12 and compared to baseline viability in each tissue. Ex vivo “response” was defined if < 1X baseline tumor cell viability. Results: With a data cutoff of 2/8/2022, all pts are enrolled: 26 evaluable for toxicity and 23 for response. Median age is 60 years (range, 32-85), and 16 (62%) are female. Grade 3-4 treatment-related adverse events (AE) have occurred in 5/26 (19%) patients: colitis, maculopapular rash, leukocytosis, and myositis/myocarditis (all N = 1); asymptomatic elevated amylase/lipase (N = 2). Overall response rate is 48% (95% CI, 27-69), and disease control rate is 96% (95% CI, 78-100). Median PFS is 7.4 months (95% CI, 5.6-NA). For the 11 pts with responses, median duration of response is 7.7 months (95% CI, 4.5-NA). Median OS is 15.1 months (95% CI, 7.7-NA). E-slices showed concordance between pts with radiographic responses and reduction in cell viability, and between non-responders and increase in cell viability. Final results will be presented. Conclusions: E + C + N appears to be effective and well-tolerated for pts with MSS, BRAFV600E metastatic CRC. Ex vivo analysis of pretreatment tissue predicted eventual clinical response in matched patients. A follow-up randomized phase II trial (SWOG 2107) to evaluate encorafenib/cetuximab with or without nivolumab in pts with MSS, BRAFV600E metastatic CRC will activate in 2022. Clinical trial information: NCT04017650.

HER3 expression in metastatic colorectal cancer: Defining the clinicomolecular profile of an emerging target

3588

Background: The success of tailored systemic therapies in treating distinct molecular subsets of patients (e.g., deficient mismatch repair, BRAF mutant, HER2 amplified) has spurred further exploration of novel targetable subsets within the heterogeneous landscape of metastatic colorectal cancer (mCRC). Human epidermal growth factor receptor 3 [HER3 (ErbB3)], a member of the HER (ErbB) receptor tyrosine kinase family, plays an important role in tumorigenesis and metastases and has emerged as a promising therapeutic target in a diverse array of cancers. For example, patritumab deruxtecan (U3-1402; HER3-DXd) is a HER3-directed antibody drug conjugate that has demonstrated clinically meaningful antitumor activity and acceptable safety profiles in metastatic breast cancer and EGFR-mutated non-small cell lung cancer. There is limited data, however, on the clinicopathological characterization of HER3 expression in mCRC. Methods: Tissue samples (surgical-metastatectomy) (N = 115) were obtained from a clinical cohort of patients (N = 99) with histologically proven mCRC and liver metastases who underwent liver resection with/without perioperative systemic chemotherapy. HER3 expression was analyzed on whole-mount preparations by immunohistochemistry (IHC). Staining was performed and visualized using the HER3 (D22C5) XP Rabbit-mAb (Cell Signaling Technology). Patients were categorized based on membranous intensity score as follows: Low with IHC 0 (absence of staining or staining in < 10% of tumor cells), 1+ (faint/barely perceptible staining in ≥10% of tumor cells) or 2+ (weak to moderate staining in ≥10% of tumor cells), or High with IHC 3+ (strong staining in ≥10% of tumor cells). Clinicomolecular and treatment data, including gender, tumor sidedness, mutational status (RAS or BRAF), and prior chemotherapy were collected by review of patient electronic medical records. Chi-squared (or Fisher’s exact) test were used to determine associations between groups. Overall survival (OS) was calculated using Kaplan-Meier method and compared using log-rank tests. Results: Among 99 analyzed patients, 98 were evaluable for HER3 expression. Of these 25.5%, 26.5%, 40.8% and 7.2% showed HER3 IHC scores of 3+, 2+, 1+ and 0, respectively. No significant association was seen with HER3 expression and clinicopathological variables, mutational status, or prior treatment. Among patients with 2 samples analyzed from the same liver surgery, there was a moderate level of heterogeneity with concordance of 78.5% (kappa 0.43). Patients with high HER3 expression had poorer OS (5-year OS: 52%; median: 90.2 months) compared to low HER3 expression (5-year OS: 85%; median: not reached). Conclusions: In this large cohort of mCRC, HER3 expression was observed in 92.8% of patients and across diverse clinical and molecular features, supporting HER3 as a promising targetable biomarker in a large subset of mCRC.

Gender disparity in authorship of clinical trials leading to cancer drug approvals between 2008 and 2018: The glass ceiling of academic oncology

11048

Background: Authorship, expressly premier positions (first, corresponding, or senior author), in peer reviewed journals is widely acknowledged as scientific credit in academia. Yet, gender inequities and biases pervade this facet of the scientific ecosystem. We reviewed the authorship of pivotal FDA trials that established the standards of care in oncology over the past decade with the goal of defining the magnitude of gender disparity in the most influential literature of the field in recent years. Methods: We collected and assessed data from the primary publication of 231 trials that enabled FDA drug approvals in hematology and oncology from July 2008 to June 2018. Author gender was assigned from listed names using statistical probability and confirmed using institutional websites and online databases (genderchecker database, biographical paragraphs, and social media). Authors where gender was not clearly identified (1.23%) were excluded. To account for equal authorship contribution, we included co-authors as distinct data points, and credit was given to reports for any women in premier authorship positions (first, corresponding, or senior author) to avoid overestimating disparity. Descriptive statistics were used, and 95% confidence intervals (95%CI) were reported using modified Wald method. Proportions were compared using Fisher-exact and Chi-squared test. Unadjusted P values of < 0.05 were considered significant. Results: A total of 4664 (98.8%) authors were included in this analysis across 227 publications. Of these, 1287 (27.6%) were female with a median of 25.9% female authorship in total per trial. Female authorship was significantly higher for non-randomized (30.4% v 26.5% for randomized, P = 0.007) and phase 1/2 trials (29.9% v 26.3% for phase 3, P = 0.009) and varied with trial size (P < 0.001), with the proportion greater in trials with ≤100 patients versus those with > 500 patients. Female authorship in fields of breast and gynecological oncology was higher (41.3%) than other cancers (26.0%, P < 0.001). Women were proportionally less likely to hold premier (9.2% v 18.2%, OR 0.46, 95%CI: 0.4 – 0.6, P < 0.001), first (3.2% v 6.3%, OR 0.49, 95%CI: 0.3 – 0.7, P < 0.001), senior (3.3% v 6.0%, OR 0.54, 95%CI: 0.4 – 0.8, P = 0.002) and corresponding (2.5% v 5.8%, OR 0.42, 95%CI 0.3 – 0.6, P < 0.001) authorship but not second author role (4.1% v 5.1%, OR 0.80, 95%CI 0.6 – 1.1, P = 0.17). Conclusions: The under-representation of women in premier authorship positions in pivotal clinical trials, demonstrated in our study, serves as a barometer of a biased academic infrastructure, amplifying existing calls to address barriers that limit the full inclusion of women in oncology.

Phase 2 randomized trial of neoadjuvant or palliative chemotherapy with or without immunotherapy for peritoneal mesothelioma (Alliance A092001)

TPS8598

Background: Peritoneal mesothelioma is a rare and poorly studied disease with few treatment options. For patients who are not surgical candidates, treatment recommendations for systemic therapy have been extrapolated from clinical trials for pleural mesothelioma that commonly exclude patients with peritoneal mesothelioma. Recently, the combination of the PD-1 inhibitor nivolumab and the CTLA-4 inhibitor ipilimumab received FDA-approval for the frontline treatment of non-resectable pleural mesothelioma. Additionally, a prospective, non-randomized phase 2 trial demonstrated activity with combined PD-L1 (atezolizumab) and VEGF (bevacizumab) blockade in peritoneal mesothelioma. In parallel, encouraging activity with combined chemo-immunotherapy has been reported in pleural mesothelioma. Given the benefits observed with immunotherapy, and the potential to improve upon those with chemotherapy and VEGF inhibition, we seek to determine whether the addition of the PD-L1 inhibitor atezolizumab improves outcomes with chemotherapy and bevacizumab in patients with newly diagnosed peritoneal mesothelioma. Methods: A092001 is a prospective, randomized phase 2 clinical trial. All patients with newly diagnosed peritoneal mesothelioma will be randomized 1:1 using a dynamic allocation Pocock-Simon procedure to receive carboplatin, pemetrexed, and bevacizumab, with or without atezolizumab, every 21 days for four cycles. Patients who are eligible to proceed with surgery after four cycles of therapy will then do so. Patients who are not eligible to proceed with surgery may receive maintenance bevacizumab and atezolizumab, or second-line atezolizumab with bevacizumab until progression of disease or toxicity. The primary objective is to determine whether frontline treatment with carboplatin, pemetrexed, bevacizumab and atezolizumab results in a superior best response rate (RR) to carboplatin, pemetrexed and bevacizumab as determined by RECIST. With 31 eligible patients per arm (62 eligible total), this randomized design has 80% power to detect an improvement in the RR from 20% to 45%, with a 1-sided significance level of 0.10 where an interim futility analysis will be conducted after 32 patients are enrolled. As stratification factors we have included eligibility for cytoreductive surgery at diagnosis, and histologic subtype. Secondary endpoints include assessment of progression-free survival, overall survival, and adverse events. As integrated biomarkers, we will determine if soluble mesothelin-related peptides and megakaryocyte potentiating factor correlate with responses. This trial was recently approved by the National Cancer Institute Central IRB and is activating at sites across the country. Support: U10CA180821, U10CA180882. Clinical trial information: NCT05001880.

Prognostic role of systemic inflammatory markers in patients with metastatic MSI-h/dMMR colorectal cancer receiving immunotherapy

3524

Background: Markers of systemic inflammation including neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), and monocyte-to-lymphocyte ratio (LMR) are prognostic in patients with metastatic colorectal cancer receiving systemic chemotherapy. The presence of liver metastases has also been hypothesized to modulate response to immunotherapy. In this study, we assess the prognostic role of these markers in patients with microsatellite high (MSI-H)/deficient mismatch repair (dMMR) tumors receiving immunotherapy for metastatic or unresectable colorectal cancer (CRC). Methods: This was a single-institution retrospective analysis of patients with dMMR/MSI-H CRC who received anti-PD-(L)1 and/or anti-CTLA-4 therapy for metastatic or unresectable disease at between 2015 and 2021 (n = 59). NLR, PLR, and LMR were calculated based on the complete blood count obtained within 1 week prior to treatment. Patient and tumor characteristics were obtained from the clinical record. Patient characteristics were compared using Fisher’s exact test and Mann-Whitney U where appropriate. Progression free survival (PFS) and overall survival (OS) were the primary endpoints and log-rank test was used for comparison of survival distribution among groups. Results: 59 patients with metastatic dMMR/MSI-H CRC were identified. Median age was 60, 53% (n = 31) had right-sided tumors, 35% (n = 35) of patients with testing available had RAS-mutated tumors, and 37% (n = 22) received prior chemotherapy. Most common sites of metastatic disease were peritoneum (n = 23, 39%) and liver (n = 17, 29%). Patients were divided into NLR-High (NLR ≥ 3, n = 20) and NLR-Low (NLR < 3, n = 39), and both groups had similar baseline characteristics. The rate of progressive disease as best response was not different in NLR-Low versus NLR-High (15% vs 30%, p = 0.3). At a median follow-up of 32 months, neither median PFS nor median OS were reached. 74% (n = 29) remained progression free at 1 year in the NLR-Low group versus 60% (n = 12) in NLR-High group which was not statistically significant (p = 0.37); 90% (n = 35) remained alive at 2 years in the NLR-low versus 80% (n = 16) in the NLR-High group (p = 0.4). Similarly, using a cut-off of 150 and 3 for PLR and LMR respectively, there was no significant difference between PFS at 1 year in the PLR-Low (n = 32) vs PLR-High (n = 27) (66% vs 74%, p = 0.58) and LMR-Low (n = 35) vs LMR-High (n = 24) (60% vs 83%, p = 0.084) groups. The presence of liver metastasis or the presence of a RAS mutation did not influence PFS at 1 year (p = 0.35 and p = 1.00, respectively). Conclusions: Markers of systemic inflammation may have a limited prognostic role for patients with dMMR/MSI-H CRC receiving immunotherapy.

Clinical outcomes following termination of immunotherapy due to long-term benefit in MSI-H colorectal cancer

3585

Background: Immune checkpoint blockade therapy improves survival in patients (pts) with microsatellite instability-high (MSI-H) advanced colorectal cancer (CRC). Oncologists often discontinue immunotherapy after 2 years of disease control based on prior trial data. Recurrence outcomes following discontinuation of immunotherapy and clinicopathologic features associated with recurrence remain underreported given the recent advent of these agents for pts with MSI-H advanced CRC. Methods: Records from pts with MSI-H CRC from MD Anderson Cancer Center who received immunotherapy between 2015-2022 and stopped after clinical benefit were reviewed. Median survival was estimated according to the Kaplan-Meier method. Associations between the event of recurrence and coexisting mutations ( KRAS, NRAS, BRAFV600E, PIK3CA, APC, TP53, POLE/POLD), metastatic site (lung, liver, lymph nodes, or peritoneum), primary tumor sidedness (right vs. left colon), and prior immunotherapy (anti-PD-(L)1 alone or with anti-CTLA-4 antibodies) were measured by Fisher’s exact tests. Results: Thirty-six pts with MSI-H CRC without progression on immunotherapy were reviewed. Of these 29 and 7 received anti-PDL1 antibody alone or in combination with anti-CTLA-4 antibody, respectively. Median exposure to prior immunotherapy was 24 months (range, 5-43). After a median follow-up of 19 months (95% CI, 14-26) after stopping immunotherapy, 30 of 36 pts (83%) remained without disease progression. For the 6 patients with progression after stopping, median time to relapse was 13 months (range, 5-31). Median disease-free survival (DFS) was not reached. The estimated 1-year, 2-year, and 3-year DFS probabilities were 90% (95% CI, 79-100), 79.1% (95% CI, 64-98), and 68% (95% CI, 47-98), respectively. Median overall survival from the time that immunotherapy was stopped was 54 months (95% CI, 47-NA). Only 1 pt died due to unrelated illness. There were no observed associations between disease recurrence and co-existing mutations, metastatic organ involvement, primary tumor sidedness, or immunotherapy used. Conclusions: Most pts with MSI-H advanced CRC who achieve initial clinical benefit and do not progress on immunotherapy do not recur after treatment is stopped. Our data suggest that favorable outcomes do occur following cessation of immunotherapy in this setting even with concomitant prognostically unfavorable clinical features (RAS, BRAFV600E mutations; liver, peritoneal metastases).

Resistance mechanisms to anti-EGFR therapy in RAS/RAF wildtype colorectal cancer varies by regimen and line of therapy

3554

Background: The conventional theory for the development of treatment resistance to anti-EGFR for metastatic colorectal cancer (mCRC) is the selective growth advantage of pre-existing therapy-resistant subclones with genomic mechanisms such as RAS mutations, leading to treatment resistance and disease progression. However, the impact of cytotoxic chemotherapy in combination with anti-EGFR on the mechanisms of resistance has not been assessed. Methods: We analyzed paired plasma samples from RAS/BRAF/EGFR wild-type mCRC patients enrolled in three large randomized phase 3 trials of anti-EGFR rechallenge in whom paired baseline and time of progression plasma samples had been collected for sequencing of ctDNA on a platform optimized for very low allele frequencies. 569 patients had paired baseline and progression ctDNA samples analyzed, including 147 in the first line study of FOLFOX +/- panitumumab, 91 patients in third line with panitumumab vs best supportive care, and 331 patients in the third line study of cetuximab vs. panitumumab. The mutational signature of the alterations acquired with therapy was evaluated. We also established colon cancer cell lines with resistance to cetuximab, FOLFOX, and SN38, and profiled transcriptional changes. Results: Using serial plasma samples, we demonstrate that patients whose tumors were treated with and responded to anti-EGFR alone were approximately 5-times more likely to develop acquired mutations at progression compared to those treated with an EGFR inhibitor in combination with cytotoxic chemotherapy (46% vs. 9%, respectively; p < 0.001). Consistent with this clinical finding, cell lines with non-genomic acquired resistance to cetuximab were cross-resistant to cytotoxic chemotherapy and vice-versa, with transcriptomic profiles consistent with epithelial to mesenchymal transition. In contrast, common acquired genomic alterations in the MAPK pathway that drive resistance to EGFR monoclonal antibodies do not impact sensitivity to cytotoxic chemotherapy. Further, contrary to the generally accepted hypothesis of clonal expansion of acquired resistance, in our work we demonstrate that baseline resistant subclonal mutations rarely expanded to become clonal at the time of progression (8%), and most remained subclonal (44%) or disappeared (49%). Conclusions: Collectively, this work outlines a model of resistance where non-genomic mechanisms of resistance common to both EGFR inhibitors and cytotoxic chemotherapy predominate in patients treated with EGFR and chemotherapy combinations. With EGFR inhibitor monotherapy, genomic acquired resistance mechanisms predominate, although only rarely through expansion of pre-existing subclones. These findings have important implications for strategies of EGFR-inhibitor rechallenge studies.

Cancer of unknown primary with gastrointestinal profiles: A favorable CUP subset

e16225

Background: Cancer of unknown primary (CUP) with a “gastrointestinal (GI) profile” appears to be a clinically distinct subset, based on immunophenotyping, specifically staining with cytokeratins 20 (CK20) and 7 (CK7), a type I and II keratin, respectively and caudal type homeobox 2 (CDX2) protein, a transcription factor expressed in nuclei of intestinal epithelial cells. However, only a limited clinicomolecular account of this entity exists. Comprehensive profiling is needed to impact personalized therapeutics and improve prognosis. Methods: We identified 497 pts using a retrospective/prospectively managed CUP database and tumor registry of pts evaluated at MD Anderson Cancer Center from 2012-2016. Pts were classified into 3 cohorts based on immunohistochemistry: lower GI profile CUP (LGI-CUP) [CK20+/CK7- or CK20+/CK7+/CDX2+], upper GI profile CUP (UGI-CUP) [CK20-/CDX2+ or CK7+/CK20+/CDX2-] and remaining were treated as a non-GI CUP (NGI-CUP) control group [CK20-/CDX2-]. Clinical and pathological data including molecular profiling, therapy and survival were logged. Fisher-exact test was used. Kaplan-Meier method was used to estimate overall survival (OS) and compared with log-rank test. Results: Among 497 pts, 316 (63.6%) had adequate immunostaining for analysis. Of these, 76 (24.1%), 75 (23.7%) and 165 (52.2%) were classified as LGI-CUP, UGI-CUP, and NGI-CUP, respectively. Median age at diagnosis for the 3 cohorts was 59, 62 and 60 years, respectively. Key baseline clinicopathological characteristics were balanced between groups except histology and Culine risk stratification. LGI-CUP were enriched for adenocarcinoma (89% v 54% v 57%, P = 0.009) and good risk group (65% v 46% v 43%, P < 0.001) compared to UGI-CUP and NGI-CUP, respectively. Median OS for the 3 cohorts were: 18.5 months (95%CI: 10.8–26.2) for LGI-CUP compared to 12.3 months (95%CI: 6.3–18.3) for UGI-CUP (P = 0.06) and 13.5 months (95%CI: 10.6–16.6) for NGI-CUP (P = 0.040). On multivariate analyses, LGI-CUP subtype emerged as an independent prognostic factor for better overall survival (HR 0.69, 95%CI: 0.5–0.9, P = 0.046) in addition to histology and Culine risk group. Among LGI-CUP, 39 pts with complete treatment data, 29 (74%) received frontline colorectal cancer specific chemotherapy (5-FU/Capecitabine-based) therapy. Median time to treatment failure was 3.6 months compared 1.8 months for those who received non-colorectal therapy (P = 0.19). For LGI-CUP, most common genomic alterations were TP53 (22%), ERBB2 (12%), KRAS (10%). For UGI-CUP, most common genomic alterations were KRAS (11%), and TP53 (9%). Conclusions: CUP pts with lower GI profile have improved overall survival compared to those with an upper GI or a non-GI immunophenotype. Identifying these CUP subsets and rational use of immunotherapy and targeted therapy may provide benefit to CUP pts, particularly as these treatments evolve for the management of known GI cancers.

Perioperative nivolumab monotherapy versus nivolumab plus ipilimumab in resectable hepatocellular carcinoma: a randomised, open-label, phase 2 trial

BACKGROUND

Hepatocellular carcinoma has high recurrence rates after surgery; however, there are no approved standard-of-care neoadjuvant or adjuvant therapies. Immunotherapy has been shown to improve survival in advanced hepatocellular carcinoma; we therefore aimed to evaluate the safety and tolerability of perioperative immunotherapy in resectable hepatocellular carcinoma.

METHODS

In this single-centre, randomised, open-label, phase 2 trial, patients with resectable hepatocellular carcinoma were randomly assigned (1:1) to receive 240 mg of nivolumab intravenously every 2 weeks (for up to three doses before surgery at 6 weeks) followed in the adjuvant phase by 480 mg of nivolumab intravenously every 4 weeks for 2 years, or 240 mg of nivolumab intravenously every 2 weeks (for up to three doses before surgery) plus one dose of 1 mg/kg of ipilimumab intravenously concurrently with the first preoperative dose of nivolumab, followed in the adjuvant phase by 480 mg of nivolumab intravenously every 4 weeks for up to 2 years plus 1 mg/kg of ipilimumab intravenously every 6 weeks for up to four cycles. Patients were randomly assigned to the treatment groups by use of block randomisation with a random block size. The primary endpoint was the safety and tolerability of nivolumab with or without ipilimumab. Secondary endpoints were the proportion of patients with an overall response, time to progression, and progression-free survival. This trial is registered with ClinicalTrials.gov (NCT03222076) and is completed.

FINDINGS

Between Oct 30, 2017, and Dec 3, 2019, 30 patients were enrolled and 27 were randomly assigned: 13 to nivolumab and 14 to nivolumab plus ipilimumab. Grade 3-4 adverse events were higher with nivolumab plus ipilimumab (six [43%] of 14 patients) than with nivolumab alone (three [23%] of 13). The most common treatment-related adverse events of any grade were increased alanine aminotransferase (three [23%] of 13 patients on nivolumab vs seven [50%] of 14 patients on nivolumab plus ipilimumab) and increased aspartate aminotransferase (three [23%] vs seven [50%]). No patients in either group had their surgery delayed due to grade 3 or worse adverse events. Seven of 27 patients had surgical cancellations, but none was due to treatment-related adverse events. Estimated median progression-free survival was 9·4 months (95% CI 1·47-not estimable [NE]) with nivolumab and 19·53 months (2·33-NE) with nivolumab plus ipilimumab (hazard ratio [HR] 0·99, 95% CI 0·31-2·54); median time to progression was 9·4 months (95% CI 1·47-NE) in the nivolumab group and 19·53 months (2·33-NE) in the nivolumab plus ipilimumab group (HR 0·89, 95% CI 0·31-2·54). In an exploratory analysis, three (23%) of 13 patients had an overall response with nivolumab monotherapy, versus none with nivolumab plus ipilimumab. Three (33%) of nine patients had a major pathological response (ie, ≥70% necrosis in the resected tumour area) with nivolumab monotherapy compared with three (27%) of 11 with nivolumab plus ipilimumab.

INTERPRETATION

Perioperative nivolumab alone and nivolumab plus ipilimumab appears to be safe and feasible in patients with resectable hepatocellular carcinoma. Our findings support further studies of immunotherapy in the perioperative setting in hepatocellular carcinoma.

FUNDING

Bristol Myers Squibb and the US National Institutes of Health.

Benchmarking Outcomes for Definitive Treatment of Young-Onset, Locally Advanced Rectal Cancer

PURPOSE

There has been an increase in the incidence of rectal cancer diagnosed in young adults (age < 50 years). We evaluated outcomes among young adults treated with pre-operative long course chemoradiation (CRT) and total mesorectal excision (TME).

METHODS

The medical records of 219 patients, age 18-49, with non-metastatic, cT3-4, or cN1-2 rectal adenocarcinoma treated from 2000 to 2017 were reviewed for demographic and treatment characteristics, as well as pathologic and oncologic outcomes. The Kaplan-Meier test, log-rank test, and Cox regression analysis were used to evaluate survival outcomes.

RESULTS

The median age at diagnosis was 44 years. CRT followed by TME and post-operative chemotherapy was the most frequent treatment sequence (n = 196), with FOLFOX (n = 115) as the predominant adjuvant chemotherapy. There was no difference in sex, stage, MSS/pMMR, or pCR by age (< 45 years [n = 111] vs. ≥ 45 years [n = 108]). The 5-year rates of DFS were 77.2% for all patients, 69.8% for age < 45 years and 84.7% for age ≥ 45 years (P = .01). The 5-year rates of OS were 89.6% for all patients, 85.1% for patients with age < 45 years and 94.3% for patients with age ≥ 45 years (P = .03). Age ≥ 45 years was associated with a lower risk of disease recurrence or death on multivariable Cox regression analysis (HR = 0.55, 95% CI 0.31-0.97, P = .04).

CONCLUSION

Among young adults, patients with age < 45 years had lower rates of DFS and OS, compared to those with age ≥ 45 years. These outcomes could serve as a benchmark by which to evaluate newer treatment approaches.

Exploratory biomarker analyses of the single-arm, phase 2 study of regorafenib plus nivolumab in patients (pts) with mismatch repair-proficient (pMMR)/microsatellite stable (MSS) colorectal cancer (CRC)

89

Background: Combination treatment with regorafenib (80–120 mg/day, PO, 3 wks on/1 wk off) plus nivolumab (480 mg IV Q4W) showed manageable safety but modest efficacy in a phase 2 study of 70 pts from North America with pMMR/MSS chemotherapy-resistant metastatic CRC (mCRC). Five pts had a partial response (PR; objective response rate [ORR]: 7%); all did not have liver metastases at baseline (n = 5/23; ORR: 22%). One pt had a confirmed complete response (CR) after the primary completion analysis of the study (ASCO 2021). This retrospective exploratory analysis investigated the potential association between specific biomarkers and anti-tumor activity, and how those biomarkers are modulated by treatment with regorafenib plus nivolumab. Methods: In formalin-fixed paraffin-embedded tumor samples obtained at baseline and Cycle (C) 2 Day (D) 8, immune-related biomarkers were assessed via immunohistochemistry (IHC), and RNA sequencing was used for gene expression profiling/gene signatures. Pre-/on-treatment blood samples were collected to measure circulating tumor DNA (ctDNA) and soluble biomarkers. Results: A total of 40 and 27 baseline tumor samples and 14 and 5 paired tumor samples at baseline/C2D8 were available for IHC and RNA sequencing, respectively. Higher baseline protein and mRNA expression of biomarkers for pre-existing immune sensitivity (eg, effector T cells) trended with anti-tumor activity. These biomarkers were expressed at lower levels in pts with liver metastases vs those without liver metastases at baseline. Cytotoxic T cell density was elevated on C2D8 but did not correlate with anti-tumor activity. Increased mean variant allelic frequency in ctDNA at C2D1 predominated in pts with progressive disease (PD), while clearance of ctDNA at C2D1 was only noted for the one pt with a CR. High clonal tumor mutational burden in ctDNA showed a numerical trend with anti-tumor activity (PD vs. SD/PR; P=0.058) and PFS (P = 0.072). Baseline serum levels of select markers related to angiogenesis (eg, vascular endothelial growth factor [VEGF] D) were associated with inferior anti-tumor activity (P = 0.002). Serum levels of immune-related soluble biomarkers (eg, tumor necrosis factor alpha) increased on treatment (P < 0.005), while levels of soluble VEGF receptor 2 decreased (P < 0.001). Conclusions: This study of pts with MSS mCRC treated with regorafenib plus nivolumab suggests that baseline tumor biomarkers for pre-existing immune sensitivity trended with anti-tumor activity, whereas select baseline peripheral biomarkers related to angiogenesis trended with inferior anti-tumor activity. Pharmacodynamics effects were observed, yet no significant correlation with anti-tumor activity was found. Due to the small sample size and retrospective nature, these analyses are hypothesis-generating. Clinical trial information: NCT04126733.

Trastuzumab deruxtecan (T-DXd; DS-8201) in patients (pts) with HER2-expressing metastatic colorectal cancer (mCRC): Final results from a phase 2, multicenter, open-label study (DESTINY-CRC01)

119

Background: T-DXd is an antibody-drug conjugate of a humanized anti-HER2 antibody bound to a topoisomerase I inhibitor by a cleavable linker. The primary analysis of DESTINY-CRC01 (DS8201-A-J203; NCT03384940), a phase 2, open-label, multicenter study of T-DXd in pts with HER2-expressing mCRC showed promising antitumor activity and a manageable safety profile (cohort A median follow-up [FU], 27.1 weeks; Siena S, ASCO 2020). We present updated longer-term efficacy and safety data. Methods: Pts had centrally confirmed HER2-expressing, RAS wild-type mCRC that progressed after ≥2 prior regimens. 6.4 mg/kg of T-DXd was administered every 3 weeks (Q3W) in 3 cohorts (A: HER2 IHC3+ or IHC2+/ISH+; B: IHC2+/ISH−; C: IHC1+). The primary endpoint was confirmed objective response rate (ORR) by independent central review in cohort A. Secondary endpoints were disease control rate (DCR; CR + PR + SD), duration of response (DOR), progression-free survival (PFS), and overall survival (OS). Results: At data cutoff (Dec 28, 2020), 86 pts (A, 53; B, 15; C, 18) received T-DXd. Median age was 58.5 y (range, 27-79), 53.5% were male, and 90.7% had left colon or rectum cancer. Median prior regimens for metastatic disease was 4 (range, 2-11). All pts had prior irinotecan; 30.2% in cohort A had prior anti-HER2 therapy. Median (m) treatment duration (all pts) was 3.0 mo (95% CI, 2.1-4.1; cohort A, 5.1 mo [95% CI, 3.9-7.6]). In cohort A (median FU, 62.4 weeks), confirmed ORR was 45.3% (24/53 pts; 95% CI, 31.6-59.6), DCR was 83.0% (44/53 pts; 95% CI, 70.2-91.9), mDOR was 7.0 mo (95% CI, 5.8-9.5), mPFS was 6.9 mo (95% CI, 4.1-8.7) with 37 (69.8%) PFS events, and mOS was 15.5 mo (95% CI, 8.8-20.8) with 36 (67.9%) OS events. These results are consistent with the primary analysis. Confirmed ORR was 43.8% (7/53 pts; 95% CI, 19.8-70.1) for pts with prior anti-HER2 therapy, 57.5% (23/53 pts; 95% CI, 40.9-73.0) for pts with IHC3+ status, and 7.7% (1/53 pts; 95% CI, 0.2-36.0) for pts with IHC2+/ISH+ status. In cohorts B and C, mPFS was 2.1 mo (95% CI, 1.4-4.1) and 1.4 mo (95% CI, 1.3-2.1); mOS was 7.3 mo (95% CI, 3.0-NE) and 7.7 mo (95% CI, 2.2-13.9), respectively. Treatment-emergent adverse events (TEAEs) of grade (G) ≥3 occurred in 65.1% of pts (56/86); the most common TEAEs were hematologic and gastrointestinal. TEAEs leading to drug discontinuation occurred in 13 pts (15.1%). 8 pts (9.3%) had interstitial lung disease (ILD) adjudicated by an independent committee as related to T-DXd (4 G2; 1 G3; 3 G5). Conclusions: T-DXd at 6.4 mg/kg Q3W showed promising activity and durability with longer-term FU in pts with HER2-expressing mCRC. The safety profile was consistent with prior results; ILD continues to be an important identified risk that requires careful monitoring and intervention as needed. These results support continued exploration of T-DXd in this patient population. Clinical trial information: NCT03384940.

Trastuzumab deruxtecan in patients with HER2-overexpressing locally advanced, unresectable, or metastatic colorectal cancer (mCRC): A randomized, multicenter, phase 2 study (DESTINY-CRC02)

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Background: Trastuzumab deruxtecan (T-DXd) is an antibody-drug conjugate comprising an anti-HER2 antibody (trastuzumab) linked to a potent topoisomerase I inhibitor (DXd). T-DXd has been approved to treat HER2-positive metastatic breast cancer (United States [US], Japan, Europe, Israel) and advanced gastric cancer (US, Japan, Israel). It is currently being evaluated in other solid tumor types including colorectal cancer. The phase 2 DESTINY-CRC01 study included patients with RAS wild-type mCRC, with a median 4 (range, 2-11) prior lines of therapy. Preliminary results in patients with HER2-overexpressing (IHC 3+ or IHC 2+/ISH+) mCRC showed T-DXd treatment (6.4-mg/kg intravenously [IV] every 3 weeks [Q3W]) resulted in a confirmed objective response rate (ORR) of 45.3% (24/53; 95% CI, 31.6-59.6%) and a median progression-free survival (PFS) of 6.9 months (95% CI, 4.1-not estimable; Siena J Clin Oncol. 2020). Activity was also seen in patients treated with prior anti-HER2 therapy. Although 5.4-mg/kg and 6.4-mg/kg doses of T-DXd have shown clinical efficacy in multiple cancer indications, the lower dose has not yet been tested in patients with HER2-overexpressing mCRC. Preliminary data also suggest T-DXd may be active in RAS mutant mCRC, unlike other anti-HER2 therapies. The DESTINY-CRC02 study aims to determine efficacy and safety of T-DXd in patients with HER2-overexpressing, RAS wild-type or mutant mCRC at 5.4-mg/kg and 6.4-mg/kg doses. Methods: DESTINY-CRC02 (NCT04744831) is a multicenter, randomized, double-blind, 2-arm, parallel phase 2 study that will be conducted in 2 stages. Eligible patients (≥18 years; ≥20 years in Japan, Taiwan, and Korea) will have HER2-overexpressing (IHC 3+ or IHC 2+/ISH+) locally advanced, unresectable or metastatic CRC and have previously received chemotherapy, anti-EGFR therapy, anti-VEGF treatment, and/or anti–PD-1/PD-L1 therapy, as clinically indicated. Prior anti-HER2 therapy will be allowed. In stage 1, patients will be randomly assigned 1:1 to receive T-DXd IV Q3W at a dose of 5.4-mg/kg (n = 40; arm 1) or 6.4-mg/kg (n = 40; arm 2). Randomization will be stratified by ECOG PS (0 or 1), HER2 status (IHC 3+ or IHC 2+/ISH+), and RAS status (wild-type or mutant). After stage 1 enrollment is complete, eligible patients in stage 2 (n = 40) will receive T-DXd 5.4 mg/kg until disease progression or other treatment discontinuation criteria are met. The study is actively enrolling and aims to enroll 120 patients across 60 sites. The primary objective is to assess efficacy of T-DXd at the 5.4-mg/kg and 6.4-mg/kg doses, with a primary endpoint of confirmed ORR by blinded independent central review. Secondary endpoints include investigator-assessed ORR, PFS, duration of response, disease control rate, clinical benefit rate, overall survival, pharmacokinetics, and safety. Clinical trial information: NCT04744831.

Circulating tumor DNA dynamics on front-line chemotherapy with bevacizumab or cetuximab in metastatic colorectal cancer: A biomarker analysis for acquired genomic alterations in CALGB/SWOG 80405 (Alliance) randomized trial

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Background: Enhanced understanding of the evolving clonal architecture under treatment stress is crucial to optimizing care and developing effective therapies in metastatic colorectal cancer (mCRC). Emergence of genomic alterations (GAs) [mutations (muts) and amplifications (amps)] in RAS, BRAF, EGFR, ERBB2, and MET have been recognized as key resistance mechanisms to anti-EGFR therapy in later lines in mCRC. Data regarding occurrence of these GAs under selective pressure in the first line setting is lacking. Methods: CALGB/SWOG 80405 was a randomized trial of bevacizumab (bev) vs cetuximab (cet) in first line mCRC. Patients (pts) with paired plasma samples (pre-treatment and post-progression) available for circulating tumor DNA (ctDNA) testing were included in this substudy. Sequencing of ctDNA was performed by Guardant360 assay in a CLIA-certified environment to detect GAs in 73 genes. RAS/BRAF status [mut vs. wild type (wt)] was based on clonal muts [pre-defined cutoff of relative MAF (rMAF) ≥ 25%] in ctDNA. Only samples with ≥1 GA were analyzed to minimize false negatives. The primary objective was to determine and compare prevalence of acquired GAs between study arms: bev (anti-VEGF) and cet (anti-EGFR). Descriptive statistics and Fisher’s exact test were used. Results: Baseline characteristics of ctDNA cohort were similar to the 80405 population. Among 133 randomized RAS/BRAF wt pts, 11 (15.3%) and 5 (8.2%) developed acquired GAs (OR 2.0, P = 0.29), in bev and cet arm, respectively. Key comparative data for pts with regard to acquired pathogenic GAs are shown in the table. Conclusions: In this randomized mCRC cohort, the ctDNA profile of acquired GAs with front line anti-EGFR chemotherapy appears to be strikingly distinct from that seen with later lines of therapy. Acquisition of GAs, classically associated with EGFR resistance in later line, was not only rare with upfront cet-chemotherapy but also comparable to bev-containing (anti-VEGF) regimen. The mechanisms of acquired resistance appear to differ when anti-EGFR therapy is administered in combination with highly active first line chemotherapy. Our findings have critical translational relevance to the timing and value of ctDNA-guided anti-EGFR rechallenge in mCRC pts, especially in those treated with anti-EGFR therapy upfront.[Table: see text]