[A case of severe colitis caused by immune checkpoint inhibitor]

A 74-year-old male with lung squamous cell carcinoma who was treated with the anti PD-1 antibody nivolumab developed frequent diarrhea four months after initiating treatment. However, his condition did not improve despite prednisolone at 20mg. Endoscopic examination revealed loss of vascular pattern, erosions, and mucosal friability, resembling ulcerative colitis. Colonoscopy revealed punch-out ulcers in the affected mucosa. Therefore, he was definitively diagnosed with severe colitis caused by immune checkpoint inhibitor treatment and cytomegalovirus colitis. Nivolumab was discontinued, and he was treated with 60mg prednisolone and ganciclovir. Although his colitis improved, he developed pneumonia and died thereafter. This case highlights adverse events that are associated with immune checkpoint inhibitors which should be treated properly.