Tumor Mutational Burden as a Biomarker for Advanced Biliary Tract Cancer.

: High tumor mutational burden (TMB-H) has been reported as a predictive marker to immunotherapy or prognostic marker in various tumor types. However, there has been little study of the role of TMB-H in advanced biliary tract cancer (BTC). : We analyzed 119 advanced BTC patients who received Gemcitabine/Cisplatin (GP) as a first-line treatment between November 2019 and April 2021. Next-generation sequencing (NGS), including TMB analysis, as a routine clinical practice was performed in 119 patients. The TruSight Oncology 500 assay from Illumina was used as a cancer panel. : Among 119 patients, 18 (18.5%) had a tumor with high TMB (≥ 10 Muts/Mb). There were no significant differences between the status of TMB and clinical outcomes with GP, including objective response rate (ORR) ( = .126), disease control rate (DCR) ( = .454), and median progression-free survival (PFS) ( = .599). The median overall survival (OS) was not different between patients with TMB-H and no TMB-H ( = .430). In subgroup analysis of 32 patients receiving immune checkpoint inhibitor (ICIs), there were significant differences in ORR ( = .034) and median PFS (  .025) with ICIs between patients with and without TMB-H. : This study revealed that TMB-H in advanced BTCs did not have a prognostic or role in the standard first-line treatment. However, TMB-H might be a predictive biomarker for response to ICIs in advanced BTC.