Abstract 1681: Correlation of BRCA1/2 mutations with response to immune checkpoint inhibitors in colorectal cancer

Abstract

Abstract Background: BRCA1 and BRCA2 are involved in homologous recombination (HR) DNA repair. They have been found to promote both tumor initiation and progression. BRCA1/2 mutations lead to genomic instability and higher tumor mutation burden (TMB). Therefore, we hypothesized that BRCA1/2 mutations may be a predictor of immune checkpoint inhibitors (ICIs) efficacy. In the present work, we explored the correlation of BRCA1/2 mutations with TMB, high microsatellite instability (MSI-H), PD-L1 expression, tumor-infiltrating lymphocytes (TILs), and ICIs efficacy in colorectal cancer. Methods: A total of 509 Chinese colorectal cancer patients were enrolled from January 2017 to January 2020 in our center. Targeted next-generation sequencing and PD-L1 immunohistochemistry (22C3 antibody) were performed in the tissues from patients. TCGA colorectal cancer cohort was used for characterizing TILs with CIBERSORT. The ICIs treatment cohort from the Memorial Sloan Kettering Cancer Center (MSKCC) was selected to analyze the association of BRCA1/2 mutations with ICIs efficacy. Results: In our cohort, the mutational frequency of BRCA1/2 genes was 9.04%. The median TMB was significantly higher in the BRCA1/2 mutations (Mut) group compared to the wild type (WT) group (52.4 vs 5.7 muts/Mb, P < 0.0001). About 41.30% of patients have MSI-H in the Mut group, while 3.67% of patients display MSI-H in the WT group (P < 0.0001). There was no association of BRCA1/2 mutations with PD-L1 expression (P = 0.172). In TCGA cohort, BRCA1/2 mutations can down-regulate regulatory T (T reg) cells (P = 0.0176) and up-regulate T follicular helper cells (P = 0.0042) and macrophages M1 (P <0.0001). In MSKCC cohort, patients in the Mut group had significantly longer median overall survival after ICIs therapy (34 vs 13 months, HR: 0.37 [95%CI: 0.19-0.72], P = 0.0234). Conclusions: Our data indicated that BRCA1/2 mutations are associated with increased TMB and MSI-H, but not with PD-L1 expression. And BRCA1/2 mutations can regulate TILs. Furthermore, BRCA1/2 mutations are associated with better response to ICIs, suggesting that they may be a useful predictor for ICIs efficacy in colorectal cancer. Citation Format: Dong-Dong Jia, Yanling Niu, Tonghui Ma, Min Shi. Correlation of BRCA1/2 mutations with response to immune checkpoint inhibitors in colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1681.