Tumor mutation burden in biliary tract cancers with ERBB family or DNA damage repair gene mutations.

Abstract

e15602 Background: Biliary tract cancers (BTCs) are aggressive malignancies associated with resistance to chemotherapy. Though immunotherapy presents a promising results based on several studies, the overall response rate is relative low. Tumor mutation burden (TMB) has been considered as a predictive biomarker of immunotherapy. However, the association between common mutations and TMB in BTCs are still unclear. Methods: We analyzed 76 BTC samples (32 cholangiocarcinoma and 44 gallbladder cancer patients) from the Cancer Genome Altas (TCGA) by whole-exome sequencing and 408 samples (276 cholangiocarcinoma and 132 gallbladder cancer patients) from Chinese clinical cohort by 381-gene targeted sequencing. The association between ERBB family members or DNA damage repair (DDR) genes and TMB was explored, respectively. TMB was defined as total number of somatic non-synonymous mutations in coding region. Results: The mutation frequency of ERBB genes was similar between the TCGA cohort and the clinical cohort (cholangiocarcinoma, 13.6% vs 10.9%; gallbladder cancer, 21.9% vs 17.4%). However, DDR mutation rate from the TCGA data was greater than that from the clinical data without consideration the pathological type (cholangiocarcinoma, 40.9% vs 21.0%; gallbladder cancer, 62.5% vs 29.5%). In cholangiocarcinoma, any ERBB gene mutation was associated with higher TMB level in TCGA cohort (P = 0.0013) and clinical cohort (P = 0.0008). Any DDR gene mutation also significantly contributed to higher TMB in two cohorts (TCGA cohort, P = 0.0001; clinical cohort, P = 0.0139). In gallbladder cancer, the same result was discovered on the significant association between ERBB genes statue and higher TMB in both two data (TCGA cohort, P = 0.0370; clinical cohort, P = 0.0008). On the contrary, higher TMB level was observed in patients carrying any DDR alterations (P = 0.0017) in TCGA cohort, but the association was not found in Chinese cohort (P = 0.2660). Besides, prognosis analysis was performed on patients in TCGA cohort. Cholangiocarcinoma patients harboring any ERBB gene mutation represent significantly poorer overall survival (median, 10.6 vs. 40.1 months; HR, 3.37; P = 0.0186). Conclusions: Chinese BTC patients may exhibit distinct gene mutations. These findings were the supplement of better comprehending BTC genomic characteristics. Further studies are needed to evaluate the efficacy of immunotherapy in BTC patients with ERBB or DDR mutation in Chinese clinical cohort.