Clinical and genomic characteristics between DDR germline and somatic mutations in pan-cancer.

Abstract

e15139 Background: The defects DNA-damage repair (DDR) genes would drive tumor formation and are associated with increased genomic instability and tumor mutational burden (TMB) in cancer. Although, alterations of DDR genes are common in tumor, the differences between the germline and somatic alterations are poorly characterized. Methods: The DNA sequencing data of 540 genes from 6174 pan-cancer patients were retrospectively collected and 276 DDR genes were analyzed. The variations were annotated as pathogenic (P), likely pathogenic (LP), and nonpathogenic (NP) according to ACMG (American College of Medical Genetics) guideline. The patients were divided into 3 groups: DDR-germline (P&LP germline variants, N = 766), DDR-somatic group (only P&LP somatic variants, N = 2923) and non-DDR group (NP variants, N = 2485). Results: In pan-cancer, 12.41% patients have germline DDR gene mutations, of which tumors with high germline mutation frequency include ovarian cancer (27/102, 26.47%), glioma (22/136, 16.18%), breast cancer (25/159, 15.72%), genitourinary cancer (17/114, 14.91%), biliary tract cancer (42/284, 14.79%), pancreatic cancer (28/193, 14.51%), colorectal cancer (95/727, 13.07%), head-neck tumors (11/85, 12.94%) and esophagus cancer (16/124, 12.90%). Meanwhile, 47.34% patients have somatic DDR gene mutations, of which tumors with high somatic mutation frequency include esophagus cancer (89/124, 71.77%), colorectal cancer (488/727, 67.13%), endometrial cancer (49/73, 67.12%), head-neck tumors (50/85, 58.82%), pancreatic cancer (111/193, 57.51%), gastric carcinoma (233/415, 56.14%), ovarian cancer (53/102, 51.96%) and biliary tract cancer (138/284, 48.59%). The most commonly germline alterations were found in TP53 (33%), PTEN (14%) and BRCA2 (14%), while in the somatic mutations, TP53 (52%) showed the highest frequency, PTEN (9%) and MSH3 (8%) followed. In pairwise comparisons of the three groups’ actionable mutations, DDR-somatic group was more likely to have alterations in TP53 (OR = 5.68), AKT3 (OR = 5.81) and APC (OR = 1.42) compared with DDR-germline group. Taken non-DDR group as reference, mutations in TP53 (OR = 5.09), PTEN (OR = 7.65), BRCA2 (OR = 5.32) were more common in DDR-germline group, but TP53 (OR = 28.90), PTEN (OR = 7.73), APC (OR = 2.68) in DDR-somatic group. The tumor mutational burden (TMB) was statistically different among the three groups (p < 2.22e−16). The DDR-somatic group exhibits the highest median TMB (5.68) compared with 1.42 in DDR-germline and 2.13 in non-DDR group. Conclusions: The differences in the mutation profile between the DDR-germline and DDR-somatic groups and the distinct actionable genes may indicate the different target-therapy choices. Besides, DDR-somatic group exhibited the highest TMB, which might indicate patients with somatic DDR alterations may better benefit from the immunotherapy.