Pembrolizumab-Related Sclerosing Cholangitis in a Patient With High Microsatellite Instability Gastric Cancer: A Case Report

Pembrolizumab is widely used to treat various malignant tumors, including gastric cancer; however, it is associated with immune-related adverse events. Among these adverse events, immune-related sclerosing cholangitis (irSC) is a rare type induced by pembrolizumab, and much remains unknown regarding its clinicopathological features and ideal management. Herein, we report the case of a 67-year-old man who received pembrolizumab for postoperative lymph node recurrence of gastric cancer. He developed irSC after the 15th course of pembrolizumab monotherapy, which was diagnosed using radiological imaging and liver biopsy. The patient was successfully treated with prednisolone. Eight months after the onset of irSC, the dose of prednisolone was tapered, and computed tomography revealed that the treatment response to pembrolizumab was maintained with progression-free lymph node metastasis despite not receiving any anticancer treatment. Understanding the characteristic imaging findings and clinicopathological features of irSC is crucial. Further accumulation of cases is necessary to establish the optimal management of irSC and to identify biomarkers that predict its risk.