Success rate of microsatellite instability examination and complete response with pembrolizumab in biliary tract cancer.

MSI examinations in BTC were successful in almost all cases, regardless of tissue sampling methods. We experienced a case in which pembrolizumab resulted in a complete response to MSI-H BTC. Since pembrolizumab for MSI-H BTC could prolong survival time, MSI examination should be performed proactively to increase treatment options.