[A Case of Cholangiocellular Carcinoma in Lynch Syndrome Treated by an Immune Checkpoint Inhibitor].

We report a case of cholangiocellular carcinoma(CCC)with high-frequency microsatellite instability(MSI-H)in Lynch syndrome that was managed using a multimodal treatment approach including an immune checkpoint inhibitor. The patient was a 74-year-old man who presented with fever as the chief complaint. He had a history of Vater's papilla cancer and colorectal cancer in Lynch syndrome. A diagnosis of CCC in the left lobe of the liver was made, and left hepatectomy and left caudate lobectomy were performed. From about 2 years and 5 months after the operation, the patient developed several episodes of cholangitis, and recurrence of CCC was diagnosed based on the results of biliary cytology. Gemcitabine and cisplatin therapy was started, but exacerbation of bile duct stenosis associated with cancer progression was observed, and pembrolizumab, an immune checkpoint inhibitor, was started as the solid cancer had an MSI-H status. The tumor markers then improved and the cholangitis subsided. We experienced a case of recurrence of CCC with MSI-H in Lynch syndrome managed by multimodal treatment including an immune checkpoint inhibitor.