A case of immune checkpoint inhibitor-related colitis with a distinctive endoscopic finding of colonic pseudolipomatosis.

A man in his 70s received anticancer chemotherapy with the anti-programmed cell death protein-ligand 1 antibody atezolizumab for non-small cell lung cancer. Ten days later, he developed diarrhea and skin rash, which were suspected to be due to immune-related adverse events, and was treated with prednisolone for 2 weeks. Five weeks after atezolizumab administration, he was admitted to our hospital for Common Terminology Criteria for Adverse Events Grade 3 diarrhea and hematochezia. Sigmoidoscopy revealed a dark red color in the mucosa of the transverse colon and multiple whitish mucosal plaques extending from the transverse colon to the rectum. Biopsy specimens revealed empty vacuoles in the lamina propria with infiltration of numerous inflammatory cells, including CD8+ T cells. Based on the findings of sigmoidoscopy and histology, the diagnosis was immune checkpoint inhibitor-related colitis with colonic pseudolipomatosis. The endoscopic findings and symptoms were markedly improved by prednisolone administration. We herein report the first case of immune checkpoint inhibitor-related colitis with characteristic endoscopic findings of colonic pseudolipomatosis. It is important to perform endoscopy and histological evaluation to determine the differential diagnosis and treatment strategy for patients treated with immune checkpoint inhibitors.