Abstract
A woman in her 70s presented with gallbladder carcinoma with liver metastases and peritoneal dissemination. After standard chemotherapy failed, a liver biopsy was performed. A FoundationOne CDx analysis showed that the tumor mutational burden (TMB) was high (34 mutations/megabase). Treatment with pembrolizumab, which is an immune checkpoint inhibitor (ICI), resulted in a partial response, and there were no significant immune-related adverse events. According to recently published reports, the frequency of TMB-high biliary tract cancer (BTC) is 3.4-4%, which makes it extremely rare. In conclusion, ICIs may be effective in patients with TMB-high BTC.