LAUSR

A 56-year-old man with advanced lung adenocarcinoma presented to the emergency department with a 6-day history of diarrhea. He was treated for lung cancer with nivolumab 3 mg/kg (144 mg/body) every 2 weeks (Q2W), followed by an increase to 240 mg Q2W for 147 weeks, for a total of 69 administrations. His dose was then increased to 480 mg/body every four weeks (Q4W) 12 days before his presentation. Clostridioides difficile toxin, cytomegalovirus antigenemia, and stool bacterial cultures were negative. Colonoscopy revealed diffusely edematous granular mucosa with mucosal redness, exudates, loss of vascular pattern, and aphtha throughout the colon but no ulcers. We diagnosed the patient with immune checkpoint inhibitor-induced colitis. We started prednisolone at a dose of 60 mg/day. His symptoms gradually improved, and he recovered without diarrhea on day ten after hospitalization. After prednisolone tapering, his symptoms did not worsen. Colonoscopy showed significant improvement on day 29, and the diffuse redness disappeared. The patient did not experience subsequent recurrence of diarrhea. He had no progression of lung cancer despite the termination of nivolumab for seven months. Here, we report a case of lung cancer in which nivolumab dose escalation after prolonged stable use triggered immune checkpoint inhibitor-induced colitis.