Evaluation of the change of outcomes over a 10-year period in patients with stage III colon cancer: pooled analysis of 6501 patients treated with fluorouracil, leucovorin, and oxaliplatin in the ACCENT database

BACKGROUND

Since 2004, adjuvant 5-fluorouracil, leucovorin, and oxaliplatin (FOLFOX or FLOX) have been the standard of care for patients with resected colon cancer. Herein we examine the change of outcomes over a 10-year period in patients with stage III colon cancer who received this regimen.

PATIENTS AND METHODS

Individual patient data from the ACCENT database was used to compare the outcomes in older (1998-2003) and newer (2004-2009) treatment eras for patients with stage III colon cancer who received adjuvant FOLFOX or FLOX. The outcomes were compared between the two groups by the multivariate Cox proportional-hazards model adjusting for age, sex, performance score, T stage, N stage, tumor sidedness, and histological grade.

RESULTS

A total of 6501 patients with stage III colon cancer who received adjuvant FOLFOX or FLOX in six randomized trials were included in the analysis. Patients enrolled in the new era group experienced statistically significant improvement in time to recurrence [3-year rate, 76.1% versus 73.0%; adjusted hazard ratio (HRadj) = 0.83 (95% CI, 0.74-0.92), P = 0.0008], disease-free survival (DFS) [3-year rate, 74.7% versus 72.3%; HRadj = 0.88 (0.79-0.98), P = 0.024], survival after recurrence (SAR) [median time, 27.0 versus 17.7 months; HRadj = 0.65 (0.57-0.74), P < 0.0001], and overall survival (OS) [5-year rate, 80.9% versus 75.7%; HRadj = 0.78 (0.69-0.88), P < 0.0001]. The improved outcomes remained in patients diagnosed at 45 years of age or older, low-risk patients (T1-3 and N1), left colon, mismatch repair proficient (pMMR), BRAF, and KRAS wild-type tumors.

CONCLUSION

Improved outcomes were observed in patients with stage III colon cancer enrolled in clinical trials who received adjuvant FOLFOX/FLOX therapy in 2004 or later compared with patients in the older era. Prolonged SAR calls for revalidation of 3-year DFS as the surrogate endpoint of OS in adjuvant clinical trials and reevaluation of optimal follow-up of OS to confirm the trial findings based on the DFS endpoints.

CLINICAL TRIALS NUMBERS

NCT00079274; NCT00096278; NCT00004931; NCT00275210; NCT00265811; NCT00112918.

An institutional series of early-onset pancreatic cancer (EOPC): Clinical outcomes and genetic and supportive care referral patterns

652

Background: The incidence of EOPC is rising and is associated with substantial implications for affected individuals and their families. Little is known about the extent of physician referrals of these patients (pts) to genetic, supportive care, and hospice services. Methods: Pts with EOPC (≤50 years) were identified using the institutional tumor registry for years 2011-2018 and retrospectively reviewed. Clinical data and rates of referral to supportive, genetic and hospice services were retrieved. Descriptive analyses were performed with 25-75% interquartile ranges (IQR) where appropriate. Overall survival (OS) was assessed using Kaplan-Meier curves and Cox Proportional Hazards modeling. Results: In total, 113 pts with EOPC and a median age of 47 years (range, 28-50) were analyzed. Of these 113 pts, 43% were female, 27% were black, and 45% had metastatic disease at initial presentation. The most commonly administered first line chemotherapy was FOLFIRINOX, with gemcitabine/nab-paclitaxel reserved for the second line. The median OS of pts with metastatic disease was 5.8 compared to 15.8 months for those without metastases. Only 28% of pts were referred to genetic services, and 72% of these underwent genetic testing. Out of the genetically tested pts, pathogenic germline mutations were confirmed for 33%. Of the original 113 pts, 41% received concurrent palliative care, which was provided at a median of 2.4 mos. (IQR, 0.7-6.8) preceding death. The median time between last chemotherapy administered and death was 2 mos. (IQR, 1-4.4), with 23% receiving treatment within the last month of life. Only 55% used hospice services prior to death for a median duration of 0.5 mos. (IQR, 0.2-1.4). Conclusions: Our study suggests that there is a tendency for late utilization of supportive and hospice care in pts with EOPC, possibly due to the desire of both pts and physicians to be more aggressive given the young age. Larger studies are warranted to elucidate barriers to concurrent supportive care, and whether formation of specialized young patient supportive care clinics would aid this situation and to avoid the use of unnecessary chemotherapy near the end of life.

Changing the landscape of germline testing in patients with pancreatic adenocarcinoma

676

Background: Results from the POLO trial demonstrated the benefits of PARP inhibition in patients (pts) with germline BRCA-mutated metastatic pancreatic cancer (PC). In 2018, ASCO and NCCN updated their guidelines to recommend that pts with a personal history of PC undergo germline testing. We examined referral patterns and frequency of germline pathogenic variants in pts with PC. Methods: A retrospective review was performed of PC pts seen at the Levine Cancer Institute (LCI) Center for Genetics between January 2010 and September 2019. Descriptive analyses were completed on demographics and appointment outcomes. Results: A total of 201 PC pts were referred; 20 canceled and 14 no-showed their appointment. The remaining 167 were seen and included in this analysis. Most pts (59%) were referred after July 2018. The median age was 65 years (range 32-90) and 19% were < 50 years. The majority of pts were female (61%). Race was most often reported as white (72%) followed by black (20%). Reported family histories were as follows: 28 (17%) claimed at least one first-degree relative with PC; 54 (32%) claimed a first, second, or third-degree relative with PC; 24 (14%) had no known family history of PC; and 95 (57%) claimed a first-degree relative with another cancer (breast [37], prostate [25], colon [18], ovarian [9], uterine [6], and gastric [2]). Germline testing was pursued by 138 (83%) pts: 25 (18%) were found to have a pathogenic variant and 50 (36%) a variant of uncertain significance. Pathogenic variants were most commonly identified in ATM (24%), BRCA2 (20%), PALB2 (12%), and CDKN2A (8%). Variants were also observed in DIS3L2, HOXB13, MITF, MUTYH (heterozygote), NTHL1 (compound heterozygote), RAD50, PRSS1, and SDHA. Among pts that had a pathogenic variant, cascade testing was performed in 11 families (44%) for 29 individuals. Conclusions: Our data suggest that the referral of PC pts to genetics has increased following updated ASCO/NCCN guidelines. However, improved adherence to genetic counseling is needed. ATM and BRCA2 were the most common germline mutations observed. More effort to increase awareness of genetic testing and its potential implications for pts and their families is warranted and might reduce cancellations and missed visits.

Change of clinical features and outcomes of adolescents and young adults (AYA) with colorectal cancer over time: Pooled analysis of 26,768 patients in the National Cancer Database (NCDB)

256

Background: The incidence of colorectal cancer (CRC) in younger patients (pts) is rising. The underlying etiology is unknown, and it is uncertain if disease biology and clinical features are changing over time. Methods: A retrospective study of pts data in the NCDB was performed to compare the clinicopathological features and outcomes of AYA with CRC over a 12-year period. Pts diagnosis period was dichotomized into older (2004 – 2009) and newer (2010 – 2015) eras. Uni- and multi-variable chi-square, logistic regression, and survival analyses were used for comparisons. Survival differences were assessed using Kaplan-Meier curves. Results: In total, 26,768 AYA (18-40yrs) with CRC were identified and included in the analysis: 45.8% (n = 12,268) from the older and 54.2% (n = 14,500) from the newer era. There were no differences between the 2 groups in gender distribution or levels of income and education. However, in the newer vs. older era, there was a greater proportion of non-white, non-black pts (7.2% vs. 6%; p = 0.0005) and pts diagnosed between the ages of 18-30 (21.1% vs. 18.8%; p < .0001). Pts in the newer era tended to have more comorbidities (8.6 vs 7.5%; p = 0.0012), left-sided tumors (77.5% vs. 76.1%; p = 0.04), and well-differentiated histology (12.0% vs. 8.3%; p < 0.0001). Newer era pts also had lower rates of metastatic disease at presentation (15.3% vs. 18.2%; p < 0.001%) and nodal involvement (54.9 vs. 58.4%; p < 0.001%). Median OS of pts with stage IV disease appears to have improved over time (24.1 vs. 22.5 mos; p = 0.014). After controlling for age, race, primary tumor site and grade, presence of comorbidities, and health insurance status, older era pts with stage IV CRC were at a 15.1% greater risk of all-cause death by year 5 compared to newer era pts (HRadj= 1.15 (1.07-1.24, p = 0.0001). Conclusions: Our data suggest that AYA with CRC in more recent years tend to present at a younger age and have a lower rate of metastatic disease. They also have improved survival. Further investigation of AYA disease etiology and biology are warranted. Continued efforts to increase awareness, promote early detection, and improve treatment options are essential.

Sociodemographic disparities in young adults with colorectal cancer (CRC): Analysis of 26,768 patients in the National Cancer Database (NCDB)

13

Background: The incidence of colorectal cancer (CRC) in young adults (YA) is rising. Impact of sociodemographic status on YA with CRC is not well described. Methods: Data obtained from the NCDB were used to examine the impact of sociodemographic status on clinicopathological features and outcomes of YA with CRC. Patients (pts) were categorized based on whether they lived in areas of low or high income and education. Logistic regression and chi-square were used to examine the differences between the groups. Results: In total, 26,768 YA (≤40 yrs) pts diagnosed with CRC between 2004 and 2016 were retrospectively studied. The majority of pts were male (51.6%), and 78.7% were white, 14.6% black, and 6.6% of other races. Of the entire cohort, 32.3% pts resided in the highest income areas (median ≥$68,000), whereas 18.4% were in the lowest ( < $38,000); 23% lived in areas that had the highest high school graduation rate ( > 93%), while 20% lived in areas of the lowest graduation rate ( < 79%); and 32.3% came from metropolitan areas, while 18.4% came from urban areas. Pts in the lowest compared to highest income and education areas were more likely to be black (OR: 6.4, 5.6-7.4), not have private insurance (OR: 6.3, 5.6-7.0), have T3/T4 stage (OR: 1.4, 1.3-1.6), have positive nodes (OR: 1.2, 1.1-1.3), be rehospitalized within 30 days (OR: 1.3, 1.1-1.6), or have a Charlson-Deyo score ≥ 1 (OR: 1.6, 1.4-1.9), and were less likely to have surgery (OR: 0.63, 0.6-0.7). After adjusting for race, insurance status, T/N stage, and Charlson-Deyo comorbidity scores, pts from lowest vs. highest income and education areas had a 24% increased risk of death (HRadj: 1.24, CI 1.1-1.44, p = 0.004), and pts from urban vs. metropolitan areas had a 10% increased risk of death (HRadj = 1.10 (1.01-1.20), P = 0.02). Pts with stage IV disease in the lowest vs. highest income populations had worse mOS (1.72 vs. 2.17 years, p < 0.001). Conclusions: YA with CRC in the lowest income and education population were more likely to have worse OS. Furthermore, regardless of income, pts in metropolitan areas seemed to have a lower risk of death likely due to greater access to care. More efforts are needed to eliminate disparities and achieve health equity.

Patterns and genomic correlates of PD-L1 expression in patients with biliary tract cancers

Background

Patients with biliary tract cancer (BTC) have a dismal prognosis and limited treatment options. Given the potential for immunotherapy in patients with BTC, we studied the expression of programmed death ligand-1 (PD-L1)/programmed death-1 (PD-1) and evaluated for associated genetic alterations in patients with BTC.

Methods

By immunohistochemistry (IHC), PD-L1 (SP142 antibody; ≥2+ and/or ≥5% staining on tumor cells considered positive) and PD-1 [NAT105 antibody; ≥1+ staining of tumor infiltrating lymphocytes (TILs) considered positive] expression was studied and next-generation sequencing (NGS) was performed using Caris Life Sciences' sequencing panel of 592 genes. A total of 652 patients with BTC were included in this study: 77 extrahepatic cholangiocarcinoma (ECC), 203 gallbladder cancer (GBC), and 372 intrahepatic cholangiocarcinoma (ICC).

Results

Of the 652 tumors 8.6% were PD-L1 positive with the following distribution: GBC 12.3% (25/203), ICC 7.3% (27/372), and ECC 5.2% (4/77). There was a statistically significant increase in BRAF, BRCA2, RNF43, and TP53 mutations in PD-L1 positive group as compared to PD-L1 negative. Among other biomarkers tested, TOP2A, tumor mutational burden (TMB) high (≥17 mutations per megabase) (10.7%), and microsatellite instability high (MSI-H) (7.1%) were increased in PD-L1 positive tumors versus PD-L1 negative tumors.

Conclusions

PD-L1 expression was noted in a small percentage (8.6%) of patients with BTC. This finding suggests potential benefit of immunotherapy in this subset of patients. Furthermore, there was a statistically significant association between PD-L1 expression and certain genomic alterations (BRAF, BRCA2, RNF43, TP53) and biomarkers (TOP2A, TMB high, MSI-H), which might direct the use of rational combination strategies and clinical trial development.

Molecular profiling of biliary cancers reveals distinct molecular alterations and potential therapeutic targets

Background

Biliary tract cancers (BTCs) are a heterogeneous group of aggressive, rare malignancies with limited standard chemotherapeutic options for advanced disease. Recent studies have demonstrated potential novel biliary cancer targets and a possible role for immunotherapy in the treatment of patients with this disease. Intrahepatic cholangiocarcinoma (IHCC), extrahepatic cholangiocarcinoma (EHCC), and gallbladder carcinoma (GBC) are frequently grouped together in clinical trials despite differences in tumor biology.

Methods

To further investigate tumor biology differences, we profiled 1,502 BTCs using next-generation sequencing (NGS), immunohistochemistry, in situ hybridization, and RNA sequencing.

Results

IHCCs had higher rates of IDH1, BAP1, and PBRM1 mutations and FGFR2 fusions; EHCCs had higher rates of KRAS, CDKN2A, and BRCA1 mutations; and GBCs had higher rates of homologous recombination repair deficiency and Her2/neu overexpression and amplification. IHCCs and GBCs had higher rates of potential positive predictive biomarkers for immune checkpoint inhibition (PD-L1 expression, high microsatellite instability, and high tumor mutational burden) than EHCCs.

Conclusions

These findings support clinical molecular profiling of BTCs to inform potential therapeutic selection and clinical trial design based on the primary tumor's site of origin within the biliary tree.

Frequency of BRCA mutation in biliary tract cancer and its correlation with tumor mutational burden (TMB) and microsatellite instability (MSI)

4085

Background: Biliary tract cancers constitute ~3% of cancers worldwide with incidence increasing, especially for intrahepatic cholangiocarcinoma (IHC). The prognosis of these tumors remains dismal and novel treatment strategies are needed to improve overall survival. BRCA mutations occur in biliary tract cancers but their frequency in distinct sites of biliary tract cancer is unknown. Moreover, no data are available correlating BRCA mutation with immunogenic markers such as TMB, MSI, or PD-L1 expression. Methods: Tumor samples from 1288 primary biliary tract cancers, comprising IHC (n = 746), extrahepatic cholangiocarcinoma (EHC) (n = 189), gallbladder (GBC) (n=353) were profiled at Caris Life Sciences, Phoenix, AZ. Testing included NextGen SEQ (MiSeq on 47 genes, NextSeq on 592 genes) and PD-L1 IHC (SP142). TMB was calculated based on somatic nonsynonymous missense mutations, and MSI was evaluated by NGS of known MSI loci. Results: BRCA mutations were detected in 3.6% (N = 46) of samples ( BRCA1 0.6%, BRCA2 3%), no differences were seen based on the site of the tumor. In GBC and IHC BRCA2 mutations (4.0% and 2.7%) were more frequent than BRCA1 (0.3% and 0.4, p < 0.05) while in EHC, similar frequency was observed ( BRCA1: 2.1%; BRCA2: 2.6%). There was no significant association with gender or age. In BRCA-mutant biliary tract cancer the most frequently mutated genes were TP53 (55.6%), ARID1A (52.2%) and KRAS (26.1%), KMT2D/C (20%, 13%) and CDKN2A(13%). Overall, BRCA mutations were associated with a higher rate of MSI-H (19.5% vs 1.7%, p = 0.001) and higher TMB in both MSI-H and MSS tumors (p<0.05). When investigated separately, BRCA association with elevated TMB was seen in IHC and EHC, but not in GBC. No correlation was seen with PD-L1 expression. TP53, KMT2D/C, RB1, PTEN, KDM6A mutations and FGFR1 amplifications were significantly higher in BRCA mutated tumors (p < 0.05). Conclusions: BRCA mutations are found in a significant subgroup of biliary tract tumors and are associated with an immunogenic tumor profile. These data provide rationale for trials testing PARP inhibitors in combination with immunotherapy and targeted therapies in patients with BRCA-mutant biliary tract cancers that are MSS.

BRCA1 genetic variant to predict survival in metastatic colorectal cancer (mCRC) patients (pts) treated with FOLFIRI/bevacizumab (bev): Results from phase III TRIBE and FIRE-3 trials

3145

Background: BRCA muts in CRC are associated with a higher tumor mutation burden irrespective of microsatellite instability, which highlights the possibility of using PARP-inhibitors(i) in CRC in the future. Early phase studies have shown that combination of PARP-i with oxaliplatin or irinotecan enhances tumor lysis in CRC. In this study, we investigated the influence of mutations in the Homologous Repair Pathway genes on survival outcomes among mCRC pts treated with oxaliplatin or irinotecan-based regimens. Methods: The impact of selected SNPs within 4 genes (BRCA1, BRCA2, RAD51, BARD1) on OS/PFS was analyzed through the OncoArray, a custom array manufactured by Illumina, on genomic DNA from blood samples of 431 pts enrolled in 2 randomized trials. TRIBE FOLFIRI/bev arm (n = 215, mPFS/OS: 9.7/26.2 mo) served as discovery cohort, FIRE-3 FOLFIRI/bev arm (n = 107, mPFS/OS: 11.5/31.4 mo) as validation and TRIBE FOLFOX/bev arm (n = 109, mPFS/OS: 10.8/26 mo) as control. Results: Significant associations were found among carriers of BRCA1 rs8176318 SNP, where C > A base change is known to reduce BRCA1 expression among CRC cells. In the discovery cohort, pts with A/A had shorter OS (22.4 vs 27.3 mo, P = .009) and PFS (7.5 vs 10.5 mo, P = .0006) compared to carriers of any C allele in both univariate and multivariate analysis. Same results were observed in pts with left-sided CRCs (PFS-7.5 vs 11 mo, P = .005; OS- 25.6 vs 32.3, P = .034) and among males (PFS- 7.5 vs 10.3 mo, P = .008; OS- 25.7 vs 31.3 mo, P = .008) in both uni and multivariate analysis. These results were also seen in the validation cohort: A/A carriers in left-sided CRCs had poor OS (26.1 vs 36.0 mo, P = .027) and PFS (9.5 vs 11.7 mo, P = .002. Males with A/A genotype also had poor OS (24.7 vs 32.5 mo, P = .028) and PFS 96.9 vs 12.2 mo; P = .0002). In the control cohort, A/A genotype carriers had poor tumor response in overall (P = .011) and left-sided disease (P = .034). These outcomes were independent of KRAS mutation status. No significant relationship was observed among females with mCRC. Conclusions: This is the first study to report that BRCA1 mut influence survival outcomes among mCRC pts, particularly among males and those with left-sided disease. Prospective trials are warranted to assess the utility of routine BRCA mut testing and the role of PARP-i in improving survival outcomes in this pt population.

Molecular differences between lymph nodes (LNs) and distant metastases (mets) in colorectal cancer (CRC)

3130

Background: LNs mets are thought to occur before distant mets. However, lymphatic and distant mets arise from independent subclones of the primary tumor, suggesting that LNs are not essential intermediaries for distant mets. We aimed to comprehensively characterize the molecular profile of LN mets and to explore the differences between LN vs distant mets and primary tumors. Methods: Tumor samples from primary CRCs, LNs, and distant mets were analyzed using NGS (MiSeq on 47 genes, NextSeq on 592 genes), immunohistochemistry. Tumor mutational burden (TMB) was calculated based on somatic nonsynonymous missense mutations, and microsatellite instability (MSI) was evaluated by NGS of known MSI loci. Results: In total, 11871 tumors samples were examined, comprising primaries (N = 5862), distant (N = 5605) and LNs mets (N = 404). The most frequently mutated genes in LNs were TP53 (72%), APC (61%), KRAS (39%), ARID1A (20%), and PIK3CA (12%). LNs showed a higher mean TMB (13 mut/MB) vs distant mets (9, P < .0001). TMB-high (17mut/MB) was more frequent in primaries and LNs vs distant mets (9.5% and 8.8% vs 4.2%, P < .001 and P = .001, respectively), as well as MSI-H (8.8% and 6.9% vs 3.7%, P < .001 and P = .017, respectively). TMB-high is significantly higher in LNs vs distant mets and primaries (P < .0001), independent of MSI-H status. Analyzing distant mets by location, LNs showed higher TMB compared to lung, liver and peritoneum mets (P < .0001). Overall, LNs showed significantly different rates of mutations in APC, KRAS, PI3KCA, KDM6A, and BRIP1 (P < .01 for all comparisons) vs primaries; while presenting a distinct molecular profile compared to distant mets ( TP53 72 vs 67%; KRAS 39 vs 50%; RNF43 7 vs 4%; ATM 5 vs 3%; KDM6A 4 vs 1%; BRCA2 4 vs 2%; MSH6 3 vs 2%; PTCH1 4 vs 1%; BRCA1 2 vs 1%; GNAS 2 vs 5%; P < .05 for all comparisons). Our cohort of 30 paired samples confirmed the molecular heterogeneity between primaries, LNs, and distant mets. Conclusions: This is the largest study to investigate the molecular differences between LNs mets, distant mets and primary tumors in CRC patients. Our data support the hypothesis that lymphatic and distants mets harbor different mutation profiles which suggests that they may arise from distinct subclones.

Association of BRCA-mutant pancreatic cancer with high tumor mutational burden (TMB) and higher PD-L1 expression

4133

Background: In the U.S. 56,000 Americans are expected to be diagnosed with pancreatic cancer in 2019. Prognosis in pancreatic cancer is poor. Therefore, new treatment strategies are urgently needed to improve survival. BRCA1 and BRCA2 mutations have been described to be the most common genetic mutations involved in familial pancreatic cancer. The optimal treatment regimen to use in BRCA-mutant pancreatic cancer has still to be established. Moreover, no data are available on association of BRCA mutation with immune-associated markerssuch as tumor mutational burden (TMB), microsatellite instability (MSI) or PD-L1 expression. Methods: Tumor samples of 2824 patients with pancreatic ductal adenocarcinoma were analyzed for BRCA mutation by NGS and for other genes (MiSeq on 47 genes, NextSeq on 592 genes) at Caris Life Sciences, Phoenix, AZ. TMB was calculated based on somatic nonsynonymous missense mutations, and MSI was evaluated by NGS of known MSI loci. PD-L1 expression was evaluated using immunohistochemistry. Results: In 4.4% (N = 124) of all pancreatic adenocarcinoma samples BRCA mutations were detected. BRCA2 mutations were more common: 3.1% (N = 89) vs 1.1% BRCA1 mutations (N = 35). BRCA mutations were associated with younger age ( BRCA1: 61 yrs for mutated vs. 64 for wild-type, p = 0.07; BRCA2: 61 yrs vs. 64, p = 0.002; both: p < 0.001). BRCA mutations were associated with higher MSI-H frequency (4.8% vs. 1.2%, p = 0.002), elevated PD-L1 expression (22% vs. 11%, p < 0.001) and higher TMB (mean 8.7 mut/MB vs. 6.5, p < 0.001); the differences remain significant in MSS tumors (p < 0.05). BRCA-mutant pancreatic carcinomas showed a significantly lower mutation frequencies in TP53 (59% vs 73%, p = 0.001), CKDN2A (13% vs 25%, p = 0.006), but higher frequencies in APC (6.5% vs 2.2%), KMT2A (1.9% vs 0.2%), AMER1 (1.9 vs 0.5%) and SETD2 (3.7% vs 0.4%) mutations (p < 0.05 for all comparisons). Conclusions: BRCA mutations are found in a significant subgroup of pancreatic ductal adenocarcinoma and these carcinomas are associated with an immunogenic tumor profile. These data suggest evaluating PARP inhibitors in combination with immunotherapy in patients with BRCA-mutant pancreatic adenocarcinoma especially in tumors that are MSS.

Re-evaluating disease-free survival (DFS) as an endpoint versus overall survival (OS) in adjuvant colon cancer (CC) trials with chemotherapy +/- biologics: An updated surrogacy analysis based on 18,886 patients (pts) from the Accent database

3502

Background: DFS with 3 years median follow-up (3yDFS) was validated as a surrogate for OS with 5 years median follow-up (5yOS) in adjuvant chemotherapy CC trials prior. Recent data showed improved survival after recurrence and OS, over time, in pts who received adjuvant FOLFOX. Hence, re-evaluation of the association between DFS and OS, as well as the optimal follow-up of OS to aid its utility in future adjuvant trials is needed. Methods: Individual patient data from 8 randomized adjuvant studies conducted from 1998-2009 were included; 3 trials tested anti-VEGF or anti-EGFR agents. Trial-level surrogacy examining the correlation of treatment effect estimates (i.e. hazard ratios) of 3yDFS and 5y to 8yOS was evaluated using both linear regression (R2WLS) and Copula bivariate (R2Copula) models. For the R2, a value closer to 1 indicates a stronger correlation. Prespecified criteria for surrogacy required either R2WLS or R2Copula ≥ 0.80 and neither < 0.7, with lower-bound 95% Confidence Interval (CI) > 0.60. The rank correlation coefficient (ρ) quantified the individual-level surrogacy. Results: Total of 18,886 pts were analyzed, with median age 60, 54% male, 83% stage III, 59% > 12 nodes examined. Median follow-up for survival ranged from 5 to 10 years across trials. Trial level correlation between 3yDFS and OS remained strong (R2WLS ≥0.74; R2Copula ≥ 0.89) and increased as the median follow-up of OS extended longer (see table). Analyses limited to stage III pts and/or trials tested biologics showed consistent results. Conclusions: 3yDFS remains a validated surrogate endpoint for 5yOS in adjuvant trials in CC pts per prespecified criteria. The correlation was strengthened with more than 6 years of follow-up for OS. [Table: see text]

Molecular landscape of colorectal cancers harboring R-spondin fusions

3588

Background: Gene fusions involving R-spondin ( RSPO) family members have been shown to drive Wnt-dependent tumor initiation in colorectal cancer (CRC). Therapies targeting Wnt pathway are being actively investigated for tumors harboring RSPO2/3 fusions. Here we set out to characterize the molecular features of CRC with and without RSPO fusions to gain insight into potential rationale combination therapy strategies. Methods: Tumor DNA sequencing of 592 genes (NextSeq, Illumina), RNA sequencing of 53 gene fusions (ArcherDx FusionPlex) and immunohistochemistry for PD-L1 on tumor cells (SP142) were tested on CRC tumors at Caris Life Sciences, Phoenix, AZ. Molecular profiles of RSPO2/3 positive (pos) were compared with negative (neg) tumors, Fisher-Exact was used for comparative analysis. Results: A total of 1356 CRC samples were analyzed. RSPO3 and RSPO2 fusions were detected in 42 (3.1%) and 4 (0.3%) samples, respectively, including 5 fusion events not previously reported (e.g., IFNGR1-RSPO3). A female predominance was seen in RSPO fusion pos vs. neg tumors (71.7% vs 45.0%, p < 0.001); no association with age or tumor sidedness was seen. RSPO2/3 fusions were mutually exclusive of MSI-high (0 vs. 5%), ERBB2 alterations (0 vs. 1% mutation, 4% amplification) and other Wnt pathway activation drivers including APC (2 vs. 75%), CTNNB1 (0 vs. 1.4%) and RNF43 (0 vs. 5.3%) mutations. Significantly higher BRAF (26 vs. 7%), RAF1 (4.5 vs. 0.4%) and SMAD4 (30 vs. 11%) mutation rates were seen in RSPO pos vs. neg tumors (p < 0.05). A universal co-activation of MAPK pathway ( KRAS, NRAS or BRAF) was seen with RSPO fusions. There was a significantly elevated PD-L1 expression in RSPO3 pos tumors (14%) compared to RSPO neg (6%, p = 0.04) and APC-mutated (5%, p = 0.02) tumors that are MSS. Conclusions: This is the largest series of CRC cases harboring an RSPO rearrangement reported to date. Comprehensive molecular analyses asserted the unique molecular landscape associated with RSPO fusions in CRC and suggested potential combinatorial approach to target Wnt/MAPK pathway. The immune modulatory effects specific to RSPO2/3 fusion revealed by PD-L1 expression suggest co-targeting Wnt pathway with PD1/PDL1 inhibitors in RSPO pos tumors.

Optimal duration of adjuvant therapy for stage III colon cancer

Colon cancer remains a major cause of mortality worldwide. Following adequate surgical resection of lymph node-positive colon cancer, the standard of care since 2004 has been to administer an oxaliplatin-containing regimen (eg, FOLFOX or CAPOX) for 6 months. These regimens have consistently improved oncologic outcomes compared with non-oxaliplatin therapies in multiple adjuvant randomized controlled trials. However, oxaliplatin-induced cumulative dose-dependent neurotoxicity is a major cause of morbidity that can persist years after treatment. The IDEA collaboration is a study that pooled data from 6 concurrent phase 3 trials comparing 3 vs 6 months of adjuvant FOLFOX or CAPOX to evaluate whether a shorter duration of therapy could maintain efficacy while reducing neurotoxicity. In this article, we review the history of adjuvant therapy in stage III colon cancer and comprehensively detail the results of the IDEA collaboration. A risk-based approach focusing on efficacy, toxicity, and patient selection is emphasized to guide discussions regarding the optimal duration of adjuvant therapy in stage III colon cancer.

Impact of Patient Age on Molecular Alterations of Left-Sided Colorectal Tumors

BACKGROUND

The incidence of colorectal cancer (CRC) in younger patients is rising, mostly due to tumors in the descending colon and rectum. Therefore, we aimed to explore the molecular differences of left-sided CRC between younger (≤45 years) and older patients (≥65).

SUBJECTS, MATERIALS, AND METHODS

In total, 1,126 CRC tumor samples from the splenic flexure to (and including) the rectum were examined by next-generation sequencing (NGS), immunohistochemistry, and in situ hybridization. Microsatellite instability (MSI) and tumor mutational burden (TMB) were assessed by NGS.

RESULTS

Younger patients (n = 350), when compared with older patients (n = 776), showed higher mutation rates in genes associated with cancer-predisposing syndromes (e.g., Lynch syndrome), such as MSH6 (4.8% vs. 1.2%, p = .005), MSH2 (2.7% vs. 0.0%, p = .004), POLE (1.6% vs. 0.0%, p = .008), NF1 (5.9% vs. 0.5%, p < .001), SMAD4 (14.3% vs. 8.3%, p = .024), and BRCA2 (3.7% vs. 0.5%, p = .002). Genes involved in histone modification were also significantly more mutated: KDM5C (1.9% vs. 0%, p = .036), KMT2A (1.1% vs. 0%, p = .033), KMT2C (1.6% vs. 0%, p = .031), KMT2D (3.8% vs. 0.7%, p = .005), and SETD2 (3.2% vs. 0.9%, p = .039). Finally, TMB-high (9.7% vs. 2.8%, p < .001) and MSI-high (MSI-H; 8.1% vs. 1.9%, p = .009) were more frequent in younger patients.

CONCLUSION

Our findings highlight the importance of genetic counseling and screening in younger CRC patients. MSI-H and TMB-high tumors could benefit from immune-checkpoint inhibitors, now approved for the treatment of MSI-H/deficient mismatch repair metastatic CRC patients. Finally, histone modifiers could serve as a new promising therapeutic target. With confirmatory studies, these results may influence our approach to younger adults with CRC.

IMPLICATIONS FOR PRACTICE

The increasing rate of colorectal cancers (CRC), primarily distal tumors, among young adults poses a global health issue. This study investigates the molecular differences between younger (≤45 years old) and older (≥65) adults with left-sided CRCs. Younger patients more frequently harbor mutations in genes associated with cancer-predisposing syndromes. Higher rates of microsatellite instability-high and tumor mutational burden-high tumors occur in younger patients, who could benefit from immune-checkpoint inhibitors. Finally, histone modifiers are more frequently mutated in younger patients and could serve as a new promising therapeutic target. This study provides new insights into mutations that may guide development of novel tailored therapy in younger CRC patients.

Characteristics of colorectal cancer (CRC) patients with BRCA1 and BRCA2 mutations

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.

Association of DNA damage response and repair genes (DDR) mutations and microsatellite instability (MSI), PD-L1 expression, tumor mutational burden (TMB) in gastroesophageal cancers

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.

Comprehensive molecular profiling of signet-ring-cell carcinoma (SRCC) from the stomach and colon

63

Background: Signet ring cell carcinoma (SRCC) is a rare variant of adenocarcinoma, accounting for about 10% of gastric cancer (GC) and 1% of colorectal cancer (CRC). SRCC is associated with poor prognosis, however little is known about the underlying molecular characteristics. Herein, we aimed to characterize the molecular features of SRCCs, and to compare the molecular profile of SRCC to adenocarcinoma; further, we assessed the impact of tumor location on the molecular profile of SRCC. Methods: SRCCs were analyzed using NGS (MiSeq on 47 genes, NextSeq on 592 genes), immunohistochemistry, and in-situ hybridization. Tumor mutational burden (TMB) was calculated based on somatic nonsynonymous missense mutations, and microsatellite instability (MSI) was evaluated by NGS of known MSI loci. Chi-square and t-tests were used for comparative analyses. Results: A total of 8,500 CRC and 1,100 GC were screened for SRCC histology. Seventy-six SRCC were identified from the CRC cohort (<1%) and 98 from the GC cohort (9%). The most frequently mutated genes in CRC-SRCC were TP53 (47%), ARID1A (26%), APC (25%), KRAS (22%), RFN43 (16%), KMT2D (12%), KMT2C (11%), SMAD4 (10%) and BRAF (10%), while in GC-SRCC were TP53 (42%), ARID1A (27%), CDH1 (11%), BAP1 (7%), PIK3CA (7%), ERBB2 (5%). When compared to non-SRCC histology (N=3522), CRC-SRCC (N=37) showed more frequently mutation in BRCA1 (11% vs 1%, P < .001) and less mutation in APC (19% vs 78%, P < .001), KRAS (22% vs 51%, P = .001) and TP53 (47% vs 73%, P = .001). Among GC cohort, SRCC (N=54) had a higher frequency of mutations in CDH1, BAP1, and ERBB2, and higher rate of amplification MYB compared to non-SRCC (N=540), although none of these differences were statistically significance. When we compared GC-SRCC vs. CRC-SRCC, only the mutation rate in APC (0% vs 25%) and KRAS (2% vs 22%) genes were significantly different (P < .001). Conclusions: Our research is the first to comprehensively characterize the molecular features of SRCC. Our data suggest that SRCCs harbor similar molecular profile, regardless the tumor location. On the other hand, significant differences were observed between SRCCs and non-SRCC tumors, therefore tailored therapy should be provided to these patients.

Gene-specific features (MLH1, MSH2, MSH6, PMS2) of mismatch repair (MMR) protein expression and somatic mutations (muts), microsatellite instability (MSI) and tumor mutational burden (TMB) in MSI-H and MMR-mutated tumor genomic profiles (TGPs)

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]

Nintedanib in metastatic appendiceal carcinoma

TPS723

Background: Appendiceal carcinomas are rare with an incidence of about 0.12 cases per 1,000,000 people per year. There is limited, mostly retrospective data in the treatment of metastatic appendiceal carcinomas. Generally, fluoropyrimidine-based therapy is used in the first line, adapting regimens for metastatic colorectal cancer. However, beyond progression, no treatments have shown clear activity. In appendiceal cancer, high vascular endothelial growth factor receptor (VEGFR)2 expression has been correlated with poor survival. Moreover, malignant ascites has been demonstrated to have elevated levels of VEGF. Nintedanib is an oral tyrosine kinase inhibitor of VEGFR which demonstrated activity in lung and ovarian cancer in clinical trials, and has undergone investigation in heavily pretreated metastatic colorectal cancer. Given the analogies between appendiceal and colorectal cancer and potentially ovarian cancer, and the limited information about the optimal treatment of metastatic appendiceal carcinomas, further investigation with nintedanib is warranted. Methods: This is a single arm, open label, investigator initiated, two-stage phase II trial (NCT 03287947) in metastatic appendiceal cancer patients after failure (defined as progression on or within 6 months or intolerance) of initial fluoropyrimidine-based therapy and at least one measurable site of disease. The trial started enrolling patients in June 2018, and up to 39 subjects will be enrolled. They will be treated with 200 mg of oral nintedanib twice daily and undergo disease evaluation every two months. The primary objective of this study is to evaluate the disease control rate (DCR), the composite of objective response and stable disease per RECIST 1.1. Secondary objectives include evaluation of safety and toxicity, objective response rate (ORR), 6-month progression free survival (PFS) and overall survival (OS). DCR, ORR & 6-month PFS will be estimated with the corresponding 95% Clopper-Pearson confidence interval. PFS & OS will be estimated using Kaplan-Meier techniques. Exploratory objectives include evaluation of serum VEGF, ascites VEGF, hypertension and paracentesis frequency in subjects with ascites at study entry. Clinical trial information: NCT 03287947.

Comparative Molecular Analyses of Esophageal Squamous Cell Carcinoma, Esophageal Adenocarcinoma, and Gastric Adenocarcinoma

BACKGROUND

Gastroesophageal cancers are often grouped together even though cancers that originate in the esophagus often exhibit different histological features, geographical distribution, risk factors, and clinical characteristics than those originating in the stomach. Herein, we aimed to compare the molecular characteristics of three different gastroesophageal cancer types: esophageal squamous cell carcinoma (ESCC), esophageal adenocarcinoma (EAC), and gastric adenocarcinoma (GAC).

SUBJECTS, MATERIALS, AND METHODS

In total, 3,342 gastroesophageal cancers were examined. Next-generation sequencing was performed on genomic DNA isolated from formalin-fixed paraffin-embedded tumor samples using the NextSeq platform. Tumor mutational burden was measured by counting all nonsynonymous missense mutations, and microsatellite instability was examined at over 7,000 target microsatellite loci. Immunohistochemistry and in situ hybridization techniques were also performed.

RESULTS

When compared with EAC and GAC, ESCC showed significantly lower mutational rates within APC, ARID1A, CDH1, KRAS, PTEN, and SMAD4, whereas more frequent mutations were observed in BAP1, CDKN2A, FOXO3, KMT2D, MSH6, NOTCH1, RB1, and SETD2. Human epidermal growth receptor 2 (HER2) overexpression was observed in 13% of EAC compared with 6% of GAC and 1% of ESCC (p < .0001). Compared with EAC and GAC, ESCC exhibited higher expression of programmed death-ligand 1 (PD-L1) (27.7% vs. 7.5% vs. 7.7%, p < .0001). We observed that FGF3, FGF4, FGF19, CCND1 (co-localized on 11q13), and FGFR1 were significantly more amplified in ESCC compared with EAC and GAC (p < .0001).

CONCLUSION

Molecular comparisons between ESCC, EAC, and GAC revealed distinct differences between squamous cell carcinomas and adenocarcinomas in each platform tested. Different prevalence of HER2/neu overexpression and amplification, and immune-related biomarkers between ESCC, EAC, and GAC, suggests different sensitivity to HER2-targeted therapy and immune checkpoint inhibition. These findings bring into question the validity of grouping patients with EAC and ESCC together in clinical trials and provide insight into molecular features that may represent novel therapeutic targets.

IMPLICATIONS FOR PRACTICE

This study highlights the genomic heterogeneity of gastroesophageal cancers, showing striking molecular differences between tumors originating from different locations. Moreover, this study showed that esophageal squamous cell carcinomas exhibit a unique molecular profile, whereas gastric adenocarcinomas and esophageal adenocarcinomas have some similarities, supporting the fact that adenocarcinomas and squamous cell carcinomas are completely different diseases, irrespective of the tumor location. This raises the question of whether treatment of gastroesophageal tumors should be determined according to histological subtype and molecular targets rather than anatomical site. These findings provide insights that could enable physicians to better select patients and inform therapeutic choices in order to improve clinical outcome.

Clinicopathological differences and survival outcomes with first-line therapy in patients with left-sided colon cancer and rectal cancer: Pooled analysis of 2879 patients from AGITG (MAX), COIN, FOCUS2, OPUS, CRYSTAL and COIN-B trials in the ARCAD database

PURPOSE

Patients with left-sided colon tumours have better survival and respond differently to biologics compared with patients with right-sided tumours. Left-sided colon tumours and rectal cancers are often grouped together. Herein, we examined the clinicopathological differences and outcomes between left-sided colon and rectal cancers.

PATIENTS AND METHODS

Data from 2879 metastatic colorectal cancer patients enrolled on six first-line clinical trials during 2004-2010 were pooled. Patients were included if the primary tumour origin was clearly defined. Progression-free survival (PFS) and overall survival (OS) were compared in the two groups after adjusting for patient and tumour characteristics, metastatic sites and the first-line regimen.

RESULTS

In total, 1374 patients with metastatic left-sided colon cancer and 1505 patients with metastatic rectal cancers were evaluated. Left-sided colon cancer patients were more likely to be female (40.1% versus 32.6%; P < 0.0001) and older (31.0% ≥ 70 years versus 25.8%; P = 0.0033) compared with rectal cancers patients. Patients with left-sided colon cancer had higher rates of liver metastases (80.9% versus 72.3%, P < 0.0001) but lower rates of lung metastases (34.2% versus 53.8%, P < 0.0001). KRAS mutations were slightly less frequent among left-sided tumours (34.8% versus 40.5%; P = 0.0103). Patients with left-sided tumours had approximately similar PFS (median 7.4 versus 6.9 months; hazard ratio [HR] 0.92, 95% confidence interval [CI] 0.87-1.03; P = 0.1998) and OS (median 17.4 versus 16.6 months; HR 0.99, 95% CI 0.91-1.07; P = 0.7597) compared with rectal cancer patients.

CONCLUSION

The site of tumour origin within the left side was not prognostic of outcomes. Moreover, neither bevacizumab nor cetuximab impacted, differently, the findings of the comparisons in outcomes between patients with left-sided colon tumours or rectal cancers.

Microsatellite instability in colorectal cancer: overview of its clinical significance and novel perspectives

Microsatellite instability (MSI) is a key biomarker in colorectal cancer (CRC), with crucial diagnostic, prognostic, and predictive implications. Testing for mismatch repair deficiency (MMR-D)/MSI is recommended during screening for Lynch syndrome, an autosomal-dominant hereditary disease that is characterized by germline mutations in the MMR genes and associated with an increased risk for several types of cancer. Additionally, MSI-high (MSI-H) status is associated with a better prognosis in early-stage CRC and a lack of benefit from adjuvant treatment with 5-fluorouracil in stage II disease. More recently, MSI has emerged as a predictor of sensitivity to immunotherapy-based treatments. The groundbreaking success of checkpoint inhibitors in MMR-D metastatic CRC has opened a new therapeutic scenario for patients with these tumors. MSI-H CRC, in both the sporadic and hereditary settings, is characterized by distinctive molecular and clinicopathologic features and represents a unique subset of CRC that is the object of growing interest and fervent research efforts. This article, an overview of the expanding role of MSI in CRC, covers its clinical significance, the available data on molecular profiling, novel perspectives on MSI testing, biomarkers in MSI-H CRC, immunotherapy resistance, and novel immunotherapy strategies.

Abstract 3618: Gene mutation and protein co-expression in melanoma and colorectal cancer by BRAF V600 mutation status

BRAF V600 oncogenic mutations are targetable in the treatment of melanoma but are more difficult to treat in colorectal cancer (CRC). The difference in the biological profile of BRAF V600 mutant melanoma and CRC compared to BRAF V600 wildtype melanoma and CRC has not been established. 5,139 tumor samples (CRC, 4007 and Mel, 1132) submitted for IHC (protein expression), ISH (gene amplification), and NGS sequencing of between 44 and 592 genes between 2009 and 2015 at a CLIA-certified laboratory (Caris Life Sciences, Phoenix, AZ) were retrospectively studied. Of these, 270 colorectal (6.7%) and 334 melanoma (29.5%) samples had BRAF V600 mutations. Genes or proteins with more than 100 samples in each BRAF wildtype and mutant group were tested for co-expression or co-mutation in each malignancy and correlations with a p-value &lt;0.01 were reported. The rate of co-mutations/expression in BRAF V600 mutant melanoma compared to BRAF wildtype melanoma was lower for 5 genes: KRAS (0% vs 3%), NRAS (0% vs 37 %), HNF1A (1% vs 2%), c-KIT (1% vs 7%), and GNAQ (0% vs 4%), and 3 proteins: MGMT by IHC (23% vs 31%), PTEN by IHC (64% vs 81%), and TOPO1 by IHC (44% vs 53%). The rate of co-mutations/expression in BRAF V600 mutant CRC compared to BRAF wildtype CRC was lower for 3 genes: KRAS (0% vs 52%), NRAS (0% vs 4%), and APC (26% vs 61%), and 2 proteins: MLH1 (66% vs 98%), PMS2 (65% vs 97%); and higher for 10 genes: HNF1A (7% vs 1%), JAK2 (2% vs 0%), MPL (1% vs 0%), AKT1 (3% vs 1%), EGFR (4% vs 1%), SMARCB1 (2% vs 0%), ATM (8% vs 4%), STK11 (3% vs 1%), PTEN (8% vs 3%), BRCA2 (18% vs 9%), and 5 proteins: EGFR (77% vs 60%), PD-1 (61% vs 42%), PD-L1 (10% vs 2%), RRM1 (63% vs 44%), and TS (58% vs 32%), and MSI by fragment analysis (35% vs 4%). In melanoma, all 8 proteins and gene mutations with significantly different expression were expressed less frequently in BRAF V600 mutants compared to wildtype. However, in CRC, 16 of 21 gene mutations and proteins were expressed more frequently among BRAF V600 mutants compared to wildtype. HNF1A was expressed more frequently in BRAF mutant CRC than in wildtype CRC but less frequently in BRAF mutant melanoma compared to BRAF wildtype melanoma. BRAF V600 mutations are associated with a biological profile that is distinct from BRAF V600 wildtype in both melanoma and colorectal cancer. Furthermore, BRAF mutant melanoma tends to have different genes and proteins co-mutated/expressed than colorectal cancer which supports previous findings suggesting differential activation of protective feedback loops. These differences in expression of gene mutations and proteins may play a role in the different responses to therapies between BRAF V600 mutant melanoma and BRAF V600 mutant colorectal cancer.

Citation Format: Matthew A. Carnell, Rebecca Feldman, Michael B. Atkins, Wafik S. El-Deiry, Michael J. Pishvaian, Mohamed E. Salem, Ari M. VanderWalde. Gene mutation and protein co-expression in melanoma and colorectal cancer by BRAF V600 mutation status [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3618.