PDCD1 and neoplasm: Pembrolizumab, a humanized anti–programmed cell death 1 (PD-1) inhibitor, is currently used for advanced solid tumors limited with microsatellite instability (MSI)-high and tumor mutational burden (TMB)-high.8–10) The prevalence is very rare with a reported incidence ranging from 2% to 9% in BTC,11,12) therefore, the clinical course with pembrolizumab for BTC remains poorly acknowledged.