Landscape of DNA damage response gene mutations in microsatellite-stable colorectal carcinoma.

e15558 Background: Colorectal carcinoma (CRC) is one of the most frequent and lethal cancers in the world. Important therapeutic progress of immune checkpoint inhibitors (ICIs) is limited to molecular niche of CRC with microsatellite-stable(MSS). The identification of genomic alterations in the DNA damage response (DDR) pathway have been recognized as pathogenic factors in hereditary cancer predisposition. Few studies showed the effects of ICIs on DDR pathway in patients with MSS CRC. Some reports suggested that DDR could reshape tumor immune microenvironment by regulating tissue repair and local immune response. Here we evaluated the molecular roles of DDR pathway and the immune microenvironment in efficacy of immunotherapy in MSS CRC. Methods: A total of 67 patients with MSS CRC were enrolled into the study. All samples were collected and detected by using NGS with a 1021 gene panel which containing 56 DDR genes (Supplementary table 1). Furthermore, comprehensive bioinformatics analysis were performed by the TCGA and MSK data. We defined pathway alteration as at least one gene in DDR pathway mutated. Results: In our results, three DDR pathway alteration showed poor prognosis (P = 0.0167) compared with DDR wild type in TCGA data (Figure 1A). The MSK data demonstrated that three DDR pathway alteration were associated with a better prognosis in MSS CRC patients through ICIs therapy (P = 0.0416, P = 0.00627, respectively, Figure 1B). The clinical data suggested the patient with DDR pathway alteration had longer OS (354.7 ± 134.0 days, PR) than the others with DDR wild type (247.1± 258.4 days, PD/SD) after PD-1-targeted therapies (P = 1.587e-08). Moreover, the patient with DDR pathway alteration showed significant longer PFS (312.3 ± 179.2 days, PR) compared with DDR wild type (163.3 ± 157.7 days, PD/SD) through immune therapies (P = 4.249e-10). Moreover, significant results of immune infiltrate deconvolution revealed resting memory CD4+ T cells were the most prevalent population between DDR pathway alteration and DDR wild type using CIBERSORT analysis (P = 0.0295, Figure 1C). The activated memory CD4+ T cells in DDR pathway alteration were lower than DDR wild type (P = 0.00858, Figure 1C-D) in patients with MSS CRC. The effects of DDR pathway alteration on immune microenvironment was also necessary for effective PD-1-targeted therapy in future study. Our results suggest that two or more DDR pathways and CD4 + T cells may serve as immunotherapy markers for advanced MSS colorectal cancer. Conclusions: Mutations in DDR pathway may serve as a biomarker for PD-1-targeted therapy through memory CD4+ T cells for MSS CRC patients, which warrants further studies.