Marshall, John L

Abstract Endocytosis regulates receptor trafficking and signaling, yet its role in colorectal cancer (CRC) remains unclear. We analyzed transcriptomic data from 15,025 CRC tumors to evaluate gene expression in clathrin-mediated endocytosis (CME) and the endosomal sorting complexes required for transport (ESCRT) pathway. Pathway-level signatures were compared across consensus molecular subtypes (CMS) and examined in relation to oncogenic signaling programs, while individual endocytosis-related genes were evaluated for associations with clinical outcomes in an independent randomized trial cohort. Expression of CME and ESCRT pathways varied by CMS, with the highest expression in CMS4 and the lowest in CMS3. Endocytosis signatures correlated with multiple oncogenic signaling pathways, including MAPK, TGF-β, WNT, PI3K, NOTCH, and angiogenesis, suggesting broad links between endocytic activity and tumor biology. In the randomized phase III CALGB/SWOG 80405 trial, low expression of AP2M1 —a core adaptor in the CME complex—was significantly associated with longer overall survival and progression-free survival in patients treated with anti-EGFR agents, but not in those receiving anti-VEGF agents. These findings suggest that endocytic trafficking may be associated with oncogenic signaling and differential therapeutic benefit in patients with metastatic CRC. The endocytosis pathway reflects biologically relevant heterogeneity in CRC and may help guide therapeutic stratification.

4122 Background: BTCs are rare and aggressive malignancies. The first-line standard of care regimen for advanced BTC (aBTC) is gemcitabine (GEM), cisplatin, and an immune checkpoint inhibitor. Although FOLFOX is a preferred second-line treatment, it is limited by neuropathy. Nal-IRI contains IRI free base in liposome nanoparticles, which shelter IRI from conversion to its active metabolite (SN-38) and increase intratumoral SN-38 compared with IRI alone. The NAPOLI-1 trial of FU/LV/nal-IRI vs. FU/LV in second-line advanced pancreatic adenocarcinoma showed an overall survival (OS) benefit. The NIFTY trial (South Korea) demonstrated median OS (mOS) benefit of FU/LV/nal-IRI over FU/LV in a second-line aBTC population (8.6 vs. 5.3 months [mo], HR 0.68, 95% CI 0.48-0.95); however, the NALIRICC trial (Germany) did not (6.9 vs. 8.2 mo, HR 1.08, 95% CI 0.68-1.72). We sought to characterize second-line FU/LV/nal-IRI efficacy in US patients (pts) with second-line aBTC. Methods: This was a single-arm, open-label, multicenter phase II study of pts with aBTC previously treated with GEM/platinum chemotherapy. Pts received nal-IRI 70 mg/m 2 IV over 90 minutes, LV 400 mg/m 2 IV over 30 minutes every 14 days, and FU 2400 mg/m 2 IV over 46 hours every 14 days. The primary objective was to determine progression-free survival rate at 4 mo (PFS 4mo ) using RECIST v. 1.1 criteria. Median PFS reported for pts receiving second-line 5-FU doublet chemotherapy was 3 mo with a PFS of 30%. FU/LV/nal-IRI was of interest if it could increase the PFS 4mo to 50% or higher. Using a one-sided α of 0.05 and 80% power, 17 of 39 evaluable pts had to be progression-free at 4 mo to detect a difference in PFS 4mo between 30% and 50%. Results: Forty-eight pts were enrolled: median age 64.5 years; 69% women; 27% gallbladder primary; 54% intra- and 19% extrahepatic. Ten pts came off study due to toxicity without disease progression before 4 mo on study and were replaced to evaluate the PFS 4mo endpoint. Of 38 evaluable pts, 18 pts (PFS 4mo 47%) were alive and progression-free at 4 mo, meeting the primary endpoint. With a median follow-up of 7.1 mo, median time to disease progression or study discontinuation due to toxicity for all pts was 2.3 mo (95% CI 1.8-4.6, PFS 4mo 38%), and for pts evaluable for the primary endpoint, median PFS was 3.5 mo (95% CI 1.8-5.5). Five pts (10%) had PFS beyond 12 mo. mOS for all pts was 7.9 mo (95% CI 5.7-11.7). Of 41 evaluable pts, the response rate was 2% (1 PR), and the disease control rate was 54%. Adverse events (AEs) were consistent with known toxicities from the FU/LV/nal-IRI regimen. Conclusions: FU/LV/nal-IRI is an effective second-line regimen for aBTC in US pts. There was significant early toxicity as 21% of pts came off study due to AEs before 4 mo. Correlative studies, including longitudinal analyses of circulating tumor DNA using banked blood specimens, are planned (NCT04005339). Clinical trial information: NCT04005339 .

Background The C-C motif chemokine receptor 5 (CCR5)/C-C motif chemokine ligand 5 (CCL5) axis plays a major role in colorectal cancer (CRC). We aimed to characterize the molecular features associated with CCR5 / CCL5 expression in CRC and to determine whether CCR5 / CCL5 levels could impact treatment outcomes. Methods 7604 CRCs tested with NextGen Sequencing on DNA and RNA were analyzed. Molecular features were evaluated according to CCR5 and CCL5 tumor gene expression quartiles. The impact on treatment outcomes was assessed in two cohorts, including 6341 real-world patients and 429 patients from the Cancer and Leukemia Group B (CALGB)/SWOG 80405 trial. Results CCR5 / CCL5 expression was higher in right-sided versus left-sided tumors, and positively associated with consensus molecular subtypes 1 and 4. Higher CCR5 / CCL5 expression was associated with higher tumor mutational burden, deficiency in mismatch repair and programmed cell death ligand 1 (PD-L1) levels. Additionally, high CCR5 / CCL5 were associated with higher immune cell infiltration in the tumor microenvironment (TME) of MMR proficient tumors. Ingenuity pathway analysis revealed upregulation of the programmed cell death protein 1 (PD-1)/PD-L1 cancer immunotherapy pathway, phosphatase and tensin homolog (PTEN) and peroxisome proliferator-activated receptors (PPAR) signaling, and cytotoxic T-lymphocyte antigen 4 (CTLA-4) signaling in cytotoxic T lymphocytes, whereas several inflammation-related pathways were downregulated. Low CCR5 / CCL5 expression was associated with increased benefit from cetuximab-FOLFOX treatment in the CALGB/SWOG 80405 trial, where significant treatment interaction was observed with biologic agents and chemotherapy backbone. Conclusions Our data show a strong association between CCR5/CCL5 gene expression and distinct molecular features, gene expression profiles, TME cell infiltration, and treatment benefit in CRC. Targeting the CCR5/CCL5 axis may have clinical applications in selected CRC subgroups and may play a key role in developing and deploying strategies to modulate the immune TME for CRC treatment.

AbstractBackground and ObjectivesPublished data comparing peritoneal metastases from appendiceal cancers (pAC) and colorectal cancers (pCRC) remain sparse. We compared pAC and pCRC using comprehensive tumor profiling (CTP).MethodsCTP was performed, including next‐generation sequencing and analysis of copy number variation (CNV), microsatellite instability (MSI) and tumor mutational burden (TMB).ResultsOne hundred thirty‐six pAC and 348 pCRC samples underwent CTP. The cohorts' age and gender were similar. pCRC demonstrated increased pathogenic variants (PATHs) in APC (48% vs. 3%, p < 0.01), ARID1A (12% vs. 2%, p < 0.01), BRAF (12% vs. 2%, p < 0.01), FBXW7 (7% vs. 2%, p < 0.01), KRAS (52% vs. 41%, p < 0.05), PIK3CA (15% vs. 2%, p < 0.01), and TP53 (53% vs. 23%, p < 0.01), and decreased PATHs in GNAS (8% vs. 31%, p < 0.01). There was no difference in CNV, fusion rate, or MSI. Median TMB was higher in pCRC (5.8 vs. 5.0 mutations per megabase, p = 0.0007). Rates of TMB‐high tumors were similar (pAC 2.1% vs. pCRC 9.0%, p = 0.1957). pCRC had significantly more TMB‐high tumors at lower thresholds.ConclusionsDespite a reduced overall TMB, pAC demonstrated mutations distinct from those seen in pCRC. These may serve as discrete biomarkers for future study.

TPS371 Background: Tucatinib (TUC), a highly selective HER2-directed tyrosine kinase inhibitor (TKI) approved in multiple regions for HER2+ metastatic breast cancer, is being developed as a novel therapy for patients (pts) with GI tumors including gastric or gastroesophageal junction adenocarcinoma (GEC). While trastuzumab (Tras) with chemotherapy is standard in the 1st-line setting for metastatic HER2+ GEC, no anti-HER2 therapy has demonstrated an OS benefit over chemotherapy as 2nd-line therapy, possibly due to loss of HER2 expression following Tras-based therapy. In GEC xenograft models, dual targeting of HER2 with TUC and Tras showed superior activity to either agent alone.(Kulukian 2020) Interim results from the MOUNTAINEER study have shown promising activity for TUC and Tras for HER2+ mCRC.(Strickler 2019) The MOUNTAINEER-02 study is evaluating the efficacy and safety of TUC with Tras, ramucirumab (Ram), and paclitaxel (Pac) in pts with HER2+ GEC in the 2nd-line setting. Methods: MOUNTAINEER-02 (NCT04499924) is a phase 2/3 study evaluating TUC + Tras with Ram and Pac. Pts receive TUC 300 mg or placebo PO BID, Tras (6 then 4 mg/kg) or placebo (IV on Days 1 and 15 of each 28-day cycle), Pac (IV on Days 1, 8, 15), and Ram (IV on Days 1 and 15). Eligible pts have locally-advanced unresectable or metastatic HER2+ GEC and have received a HER2-directed antibody and 1 prior line of therapy for advanced disease. Pts must be ≥18 years of age, with an ECOG ≤1, and have had no prior exposure to Ram, anti-HER2 or anti-EGFR TKI, HER2-directed antibody-drug conjugates, or taxanes ≤12 months before enrollment. Due to the potential impact of TUC on Pac metabolism, the study will include an initial Pac dose optimization stage. The open-label phase 2 part will determine the recommended dose of Pac (60 or 80 mg/m²) combined with TUC, Tras, and Ram in 6-18 pts, and evaluate safety and activity of the regimen in Cohorts 2A and 2B (30 pts each). The randomized, double-blind, phase 3 part will compare the efficacy and safety of TUC and Tras (Arm 3A; ̃235 pts) vs. placebo (Arm 3B; ̃235 pts), both in combination with Ram and Pac, and also evaluate activity of TUC with Ram and Pac (Arm 3C; ̃30 pts). The dual primary phase 3 endpoints are OS and PFS per investigator, with confirmed ORR as a key secondary endpoint. HER2 status is determined at baseline using a blood-based NGS assay, and IHC/ISH of fresh or archival tumor biopsies, if available. Pts must be HER2+ by blood-based NGS in Cohort 2A and phase 3; in Cohort 2B, pts must be HER2+ in a biopsy taken post-progression during/after 1st-line therapy, but HER2-negative by blood-based NGS. Disease assessments per RECISTv1.1 will occur q6 weeks for 36 weeks, then q9 weeks. The pharmacokinetics of TUC, Pac, and their metabolites will be evaluated in a subset of pts, including a cohort with gastrectomies. Enrollment in phase 2 is ongoing. Clinical trial information: NCT04499924.

Abstract Purpose: Mutations in KRAS/NRAS (RAS) predict lack of anti-EGFR efficacy in metastatic colorectal cancer (mCRC). However, it is unclear if all RAS mutations have similar impact, and atypical mutations beyond those in standard guidelines exist. Experimental Design: We reviewed 7 tissue and 1 cell-free DNA cohorts of 9,485 patients to characterize atypical RAS variants. Using an in vitro cell-based assay (functional annotation for cancer treatment), Ba/F3 transformation, and in vivo xenograft models of transduced isogenic clones, we assessed signaling changes across mutations. Results: KRAS exon 2, extended RAS, and atypical RAS mutations were noted in 37.8%, 9.5%, and 1.2% of patients, respectively. Among atypical variants, KRAS L19F, Q22K, and D33E occurred at prevalence ≥0.1%, whereas no NRAS codon 117/146 and only one NRAS codon 59 mutation was noted. Atypical RAS mutations had worse overall survival than RAS/BRAF wild-type mCRC (HR, 2.90; 95% confidence interval, 1.24–6.80; P = 0.014). We functionally characterized 114 variants with the FACT assay. All KRAS exon 2 and extended RAS mutations appeared activating. Of 57 atypical RAS variants characterized, 18 (31.6%) had signaling below wild-type, 23 (40.4%) had signaling between wild-type and activating control, and 16 (28.1%) were hyperactive beyond the activating control. Ba/F3 transformation (17/18 variants) and xenograft model (7/8 variants) validation was highly concordant with FACT results, and activating atypical variants were those that occurred at highest prevalence in clinical cohorts. Conclusions: We provide best available evidence to guide treatment when atypical RAS variants are identified. KRAS L19F, Q22K, D33E, and T50I are more prevalent than many guideline-included RAS variants and functionally relevant.

TPS252 Background: Tucatinib (TUC), a highly selective HER2-directed TKI recently approved for HER2+ metastatic breast cancer (MBC), is being developed as a novel therapy for patients (pts) with metastatic colorectal cancer (mCRC) and other GI tumors. While trastuzumab (Tras) with chemotherapy is standard in the 1st-line setting for metastatic HER2+ gastric or gastroesophageal junction adenocarcinoma (GEC), no anti-HER2 therapy has demonstrated an OS benefit over chemotherapy in 2nd-line, possibly due to loss of HER2 expression following Tras-based therapy. In GEC xenograft models, dual targeting of HER2 with TUC and Tras showed superior activity to either agent alone. Interim results from the MOUNTAINEER study have shown promising activity for TUC and Tras in HER2+ mCRC. The MOUNTAINEER-02 study is evaluating the efficacy and safety of TUC in combination with Tras, ramucirumab (Ram), and paclitaxel (Pac) in pts with HER2+ GEC. Methods: MOUNTAINEER-02 (NCT04499924) is a phase 2/3 study evaluating TUC and Tras with the 2nd-line standard of care, Ram and Pac. Pts receive TUC 300 mg or placebo PO BID, Tras (6 then 4 mg/kg) or placebo (IV on Days 1 and 15 of each 28-day cycle), Pac (IV on Days 1, 8, 15), and Ram (IV on Days 1 and 15). Eligible pts have locally-advanced unresectable or metastatic HER2+ GEC, have received a HER2-directed antibody, and 1 prior line of therapy for advanced disease. Pts must be ≥18 years of age, with an ECOG ≤1, and have had no prior exposure to Ram, anti-HER2 or anti-EGFR TKI, HER2-directed antibody-drug conjugates, or taxanes ≤12 months before enrollment. Due to the potential impact of TUC on Pac metabolism, the study will include an initial Pac dose finding stage. The open-label phase 2 part will determine the recommended dose of Pac (60 or 80 mg/m²) combined with TUC, Tras, and Ram in 6-12 patients, and evaluate the safety and activity of the regimen in Cohorts 2A and 2B (30 patients each). The randomized, double-blind, phase 3 part will compare the efficacy and safety of TUC and Tras (Arm 3A; ~235 patients) vs. placebo (Arm 3B; ~235 patients), both in combination with Ram and Pac, and also evaluate activity of TUC with Ram and Pac (Arm 3C; ~30 patients). The dual primary phase 3 endpoints are OS and PFS per investigator, with confirmed ORR as a key secondary endpoint. HER2 status is determined at baseline using a blood-based NGS assay, and IHC/ISH of fresh or archival tumor biopsies, if available. Pts must be HER2+ by blood-based NGS in Cohort 2A and phase 3; in Cohort 2B, pts must be HER2+ in a biopsy taken post-progression during/after 1st-line therapy, but HER2-negative by blood-based NGS. Disease assessments per RECISTv1.1 will occur q6 weeks for 36 weeks, then q9 weeks. The pharmacokinetics of TUC, Pac, and their metabolites will be evaluated in a subset of pts, including a cohort with gastrectomies. Enrollment is ongoing in the U.S. Clinical trial information: NCT04499924.

4020 Background: Adjuvant chemotherapy (AC) presents a substantial patient education challenge to medical oncologists (MOs). Findings from our 2005 pilot survey suggest that a significant fraction of colorectal cancer (CRC) survivors are willing to undergo AC for modest treatment benefits, but their understanding of risks and benefits may be suboptimal. This project attempted to validate these findings by surveying patients with CRC (Pts) who previously received AC. Methods: 150 Pts who received AC for CRC in the last 5 years were recruited to listen to an audio program on AC featuring interviews with clinical investigators (CIs) and Pts who received AC. Based on this input, Pts were asked whether they would undergo the same AC again for varying absolute treatment benefits. A corresponding survey asked 24 CRC CIs and 150 MOs to predict how patients would respond. The survey also queried Pts about their expectations of and experiences with AC side effects. Results: About 1/3 of Pts would be treated again with AC for a 1% absolute reduction in recurrence risk (ARRR), and about 2/3 believed a 5% ARRR would justify treatment. There were no statistically significant differences between responses of males and females or between Pts receiving oxaliplatin (OX) and those receiving other regimens. ( Table 1 ) The corresponding estimates of CIs and MOs were lower. Additionally, AC side effects were different than expected: 57% and 66% of Pts experienced less GI toxicity and alopecia, respectively, while 38% and 46% of Pts receiving OX experienced greater cold intolerance and numbness. Conclusions: Many potential obstacles exist in communicating with Pts about AC including heterogeneity in Pts’ attitudes towards risk/benefit trade-offs and preconceptions about treatment side effects. The next step in this initiative will be to examine these issues prospectively by evaluating the impact of an audio/web education supplement on the decision-making process. [Table: see text] No significant financial relationships to disclose.

606 Background: Between 3-5% of CRC patients have BRCA1/2 pathogenic mutations. This study aims to identify associations between BRCA1 and BRCA2 mutations and clinical characteristics in CRC. Methods: A total of 6396 CRC tumor samples were tested with Next-Generation Sequencing (NGS) on a 592-gene panel, pathogenic or presumed pathogenic variants were counted as mutations (mt). Microsatellite instability (MSI) and tumor mutational burden (TMB) were tested by NGS. Statistical correlations were investigated using ANOVA, Chi-square and t-test. Results: Among tumors sampled, 53% derived from male patients and median age was 60 years. BRCA1 mt were detected in 1.1% (n = 72) of tumors, while BRCA2 in 2.8% (n = 179). BRCA1 mt were more frequent in women (W;65%) than men (M;35%) (p = 0.0019) while no relationship with sex was seen for BRCA2 mt (42% F vs. 58% M). No significant associations with age were noticed. Majority of pathogenic mt in BRCA1 (52%; n = 34) and BRCA2 (62%; n = 103) occurred in MSI-High (MSI-H) cases. MSI-H pts had more frameshift mt in both BRCA1/2 than MSS pts. MSS cases had lower rates of BRCA1 and 2 pathogenic mt (44% and 37%, respectively). Right-sided tumors were significantly associated with BRCA1 (p = 0.0056) and BRCA2 (p < 0.0001) mt in MSI-H cases only. BRCA1/2 mt were associated with higher TMB in all CRCs, including MSI-H and MSS cases (p < 0.001). POLE mt (n = 31) were associated with higher BRCA1/2 mt rates (9.6%, 55% respectively). Among MSS cases with POLE wild-type status, BRCA1 (p = 0.0269) and BRCA2 (p = 0.0151) mt were associated with high TMB and combining both BRCA1/2 mutations led to an even higher TMB (3.6%; p = 0.001). Conclusions: This is the first study to show that BRCA1/2 mutations are more frequent in MSI-H, and independently associated with higher TMB, pathogenic POLE mutations, and right-sided tumors in MSI-H CRCs. Given their relationship with TMB, the presence of BRCA1/2 mutations may be potential predictive biomarkers for checkpoint or PARP inhibitors in CRC, a finding that should be prospectively evaluated.

60 Background: DDR mutations are associated with higher neoantigen load and tumor infiltrating lymphocytes, and are a potential biomarker for immunotherapy. We investigated the association of DDR mutations in gastric (GC), esophageal (EC), and gastroesophageal junction (GEJ) cancers with MSI, PD-L1, and TMB, known predictors for immune checkpoint inhibitors. Methods: 20 DDR mutations were tested by Next-Generation Sequencing (NGS) with a 592-gene panel on a total of 1935 (709 EC; 831 GC; 355 GEJ) cancers. TMB was assessed by NGS, MSI by NGS or fragment analysis, and PD-L1 by IHC (22c3 for CPS or SP142). Results: GC had the highest DDR mutation rate compared to EC and GEJ (27% vs. 20%, p = 0.0005 and 17%, p = 0.0002, respectively). MSI-High (MSI-H) was significantly more common in the DDR mutated cohort (DDR-M) compared to non-mutated cancers (18% vs. 1%; p < 0.0001). TMB-High (≥ 10 mutations/megabase [mt/MB]) was higher in DDR-M (35% vs. 21%; p < 0.0001); in DDR-M cohort, GC had the highest TMB compared to DDR-M EC and GEJ (mean: 13.8 vs. 9.4 vs. 10 mt/MB, respectively; p < 0.0001). DDR mutations were more frequent in the PD-L1 combined positive score (CPS) ≥ 50 group than CPS 0 (42.9% vs. 24%; p = 0.037) and CPS 1-9 (42.9% vs. 20.6%; p = 0.005). ARID1A, ATRX, BRCA2, and PTEN were the most prevalent DDR mutations in MSI-H (87%, 31%, 25%, 24%, respectively); ARID1A, ATRX, BRCA2, and PTEN in TMB-High (47%, 7.7%, 6.7%, 6.8%) and ARID1A, BRCA2, RAD50, and WRN in PD-L1 high (CPS ≥ 10) (48.5% vs. 5.2% vs. 2.5% vs. 3.4%). Conclusions: MSI-H, TMB-high and high PD-L1 expression were significantly more prevalent in the DDR-M cohort compared to non-DDR-mutated cancers, most pronounced in GC. Alterations in ARID1A, ATRX, BRCA2, and PTEN were correlated with MSI-H and TMB-high while ARID1A, BRCA2, RAD50, and WRN were correlated with increased PD-L1 expression. Our findings may help identify patients for tailored immunotherapy approaches in future clinical trials.