Citations

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.

588 Background: CALGB/SWOG 80405 found no difference in overall survival (OS) or progression-free survival (PFS) in 1137 patients with KRAS wild-type metastatic colorectal cancer (mCRC) treated with either the anti-VEGF agent bevacizumab (Bev) or the anti-EGFR agent cetuximab (Cet) in combination with chemotherapy (FOLFOX or FOLFIRI) as first-line therapy. Additional molecular biomarkers are required for the optimization of treatment choices for patients with mCRC. Methods: Levels of 24 proteins were assayed in EDTA-plasma samples using multiplex ELISA techniques. Plasma samples were collected at baseline and cycle 2 day 1 (C2D1). Analyses of baseline markers have been presented previously. Changes from baseline to C2D1 were expressed as an L-ratio (LR, log2 of C2D1 divided by baseline measure). LRs dichotomized at 0 were analyzed for potential prognostic and predictive effects on OS and PFS using Cox models while adjusting for confounders (post-hoc optimized cutpoints were used for PLGF, TIMP1, VCAM1, and VEGFR3 due to skew in the distributions of these markers). P-values are not corrected for multiple testing. Results: Baseline and matched C2D1 samples from 446 patients (212 Bev/234 Cet) were available for analysis. Thirteen markers were differentially modulated between arms (p < 0.05). Early increases in CD73 (p = 0.001), ICAM1 (p = 0.022), TIMP1 (p = 0.001), TSP2 (p = 0.024), and VEGFR3 (p = 0.006) were prognostic for shorter OS. Increases in ICAM1 (p = 0.008), TIMP1 (p = 0.042), and TGFB1 (p = 0.039) were prognostic for shorter PFS. Changes in VEGFR3 (pint = 0.097) and TGFBR3 (pint = 0.052) were predictive for OS and PFS, respectively. No other markers were predictive for OS or PFS (p < 0.1). Conclusions: Changes in circulating plasma protein biomarkers observed in patients enrolled in CALGB/SWOG 80405 were both prognostic and predictive for OS and PFS and warrant further study. Such changes could provide valuable information and help guide treatment decisions. Support: U10CA180821, U10CA180882, U10CA180888, U10CA180830; ClinicalTrials.gov: NCT00265850. [Table: see text]

505 Background: MSI is a tumor biomarker for immunotherapy efficacy that is closely associated w/deficient MMR, and is also variably associated w/somatic muts of the MMR genes, loss of MMR protein expression by immunohistochemistry (IHC), and high TMB. Germ-line muts (Lynch syndrome/LS) in the 4 MMR genes are recognized to have distinct cancer spectrums/penetrance in LS, yet across all tumors, gene-specific variability in MMR IHC, MMR muts, and TMB is understudied. Methods: Results of TGPs performed by Caris Lifesciences (2015-17) were analyzed in colorectal (CRC), endometrial (EC) and all other cancers/tumors (OT) as: 1) all MSI-H tumors (n = 1057) and 2) all tumors w/ ≥1 mut in an MMR gene (n = 470). A subset of cases had IHC for MMR protein and PD-L1 expression. MSI and TMB were determined by NGS. Results: Characteristics of MSI-H tumors and tumors w/ ≥1 MMR mut are seen in the Table. A single MSH6 mut [F1088fs] in a coding microsatellite represented 31% of all MMR muts detected. F1088fs was found in 58% tumors w/MLH1/PMS2 loss (IHC) but only 25% w/MSH2/MSH6 loss (p < 0.001), was more commonly seen in EC vs CRC/OT (p < 0.001), and was negatively associated w/somatic POLE mut (p = 0.002). Distinct mut signatures in the MMR genes (e.g. GLUàSTOP) were seen in tumors w/POLE muts and DNA repair genes. Conclusions: MSI-H and MMR mutated tumors demonstrate marked gene-specific heterogeneity in IHC patterns, TMBs, and somatic muts that may be relevant to treatment selection, resistance, and response. [Table: see text]

726 Background: Primary tumor location is an important prognostic factor in mCRC. Efficacy differences with EGFR antibodies by tumor location show a predictive effect (Arnold et al. Ann Oncol 2017). Two first-line (1L) pivotal bev trials showed the prognostic value of sidedness (Loupakis et al. J Natl Cancer Inst 2015). In this exploratory study, further analysis of the predictive effect of bev is presented. Methods: Data from two randomized phase III studies (NO16966 [NCT00069095], AVF2107g [NCT00109070]) of bev+CT vs CT-alone as 1L treatment for mCRC were analyzed retrospectively. Patients (pts) with sidedness information available were included; pts from NO16966 (part 1) randomized to CT only were excluded. Sidedness was identified by case report forms. Results: Sidedness was determined in 1590 pts (27% Right and 73% Left) out of 2214 pts total (Table). In the pooled analysis, PFS improved with bev+CT compared to CT only in both right-sided (HR=0.75; 95% CI 0.61, 0.93) and left-sided (HR=0.76; 95% CI 0.67, 0.86) mCRC with similar magnitude of benefit in both sides. OS also improved with bev+CT in right-sided (HR=0.82; 95% CI 0.65, 1.03) and left-sided (HR=0.85; 95% CI 0.74, 0.98) pts. Conclusions: This exploratory subgroup analysis of two pivotal studies indicates that the effect of bev is independent of tumor location in mCRC patients. Survival outcomes. Clinical trial information: NCT00069095 and NCT00109070. [Table: see text]

638 Background: Colorectal cancer (CRC) is a heterogeneous disease with distinct molecular subtypes in part based on RAS mutational status. It is plausible that RAS mutations are differentially distributed between CC and AA and may contribute to poor outcomes in AAs with CRC. Methods: We did a retrospective analysis of CALGB/SWOG 80405 trial patients. We divided the entire cohort into 2 groups: a) Common RAS: mutation in KRAS exon 2, codon 12 or 13; b) Extended RAS: any NRAS mutations or mutation in KRAS except those listed above. We then analyzed these two subgroups for association between RAS mutations and race (3 categories: Caucasian, AA, Others) using chi-square test for univariate analyses and logistic regression for multivariate analysis. We also analyzed the effect of extended RAS testing on prognosis of metastatic CRC by estimating the overall survival (OS) using Kaplan-Meier method and 95% confidence interval (CI). Cox proportional-hazard model was used for multivariate analyses. Results: There were 1729 CRC patients in common RAS group of which 357 (20.6%) had mutations present. Extended RAS group had 621 patients of which 95 (15.5%) had mutations present. There was no significant difference in the rate of common RAS mutations between CC and AA (20.5% vs. 24%, p=0.22). However, extended RAS mutations were significantly more in AA as compared to CC (25% vs. 14%, p=0.02). Multivariate analysis adjusted for age, gender, prior adjuvant chemotherapy and pelvic radiation confirmed higher odds of extended RAS mutation in AA compared to CC (adjusted OR 1.12; 95% CI 1.01-1.23; p=0.02). The median OS in patients with an extended RAS mutation was shorter as compared to those without extended RAS mutation (25.3 vs. 31.9 months; HR 1.26; 95% CI 0.99-1.62; p=0.05). Multivariate analyses adjusted for age, gender, race, prior adjuvant chemotherapy and pelvic radiation showed a trend towards longer OS in patients without extended RAS mutation as compared those with extended RAS mutation (adjusted HR= 1.24, 95% CI, 0.97-0.1.58, p=0.08). Conclusions: Extended RAS mutations are significantly more common in AA as compared to CC. Additionally, presence of extended RAS mutation may confer a poor prognosis in CRC patients.

611 Background: Regorafenib is an oral multikinase inhibitor with survival benefit in refractory mCRC patients (pts). Toxicities such as Palmar-plantar erythrodysesthesia syndrome (PPES), fatigue and hypertension (HTN) have limited its use. Despite absence of supportive data, various dosing or interval scheduling have been implemented into clinical practice. Methods: A randomized phase II study of regorafenib dose-escalation (Arm A: 80 mg/day, weekly dose escalation if no significant drug-related toxicities, up to 160 mg/day) vs. standard dose (Arm B: 160 mg/day) in pts with mCRC for 21 days of a 28-day cycle. Pts were randomized 1:1:1:1 to arms A1 and B1 (Pre-emptive Clobetasol for PPES); A2 and B2 (Reactive Clobetasol). The primary endpoint was the proportion of patients who completed 2 cycles of treatment and initiated the 3rd in Arm A (Pooled A1 + A2) vs. Arm B (Pooled B1 + B2). Superiority for Arm A was to be declared if the one-sided p-value calculated using Fisher’s exact method was less than 0.2. Results: From June 2015 to June 2017, 123 pts were randomized with 116 (A = 54, B = 62) evaluable for the primary endpoint. Demographic data were well balanced with overall median age of 61yrs (range: 29-81), M/F (61/39%) and ECOG PS 0/1 (37/63%) and KRAS MT/WT/UNK (47/44/9%).The study met its primary endpoint with 43% of pts on Arm A initiating the 3rd vs. only 25% of pts Arm B [one-sided p-value 0.028]. Median Overall Survival (OS) was improved in Arm A vs. Arm B (9.0 mos vs. 5.9 mos; p = 0.094). Median Progression Free Survival (PFS) was 2.5 mos for Arm A vs. 2.0 mos for Arm B (p=0.553). Overall rates of grade 3/4 toxicity were more favorable for Arm A vs. Arm B (% PPES 15 vs. 16, HTN 7 vs. 15 and fatigue 13 vs. 18, respectively). Multiple QOL parameters were improved in A vs. B primarily at week 2 of the first cycle. Conclusion: A strategy with weekly dose escalation of regorafenib from 80 mg to 160 mg/day was found to be superior to a starting dose of 160 mg/day. These results establish a new standard for optimizing regorafenib dosing. Further data on outcomes of preemptive vs. reactive clobetasol strategies are undergoing analysis and will be presented later. Clinical trial information: NCT02368886.