An extremely rare case of nivolumab‐associated macroscopic duodenitis with spontaneous regression

An 82‐year‐old man was presented to our hospital due to epigastric and right hypochondrial pain 17 weeks after the initiation of intravenous treatment with nivolumab for recurrent lung adenocarcinoma as multiple lung and sternal metastases. Urgent gastroscopy revealed macroscopic duodenitis such as severe erythema, oedema, black‐coloured erosions, and ulcers located throughout the second portion of the duodenum, which was confirmed by abdominal computed tomography as circumferential thickening of the duodenal wall. Those lesions were pathologically considered as non‐specific inflammation and spontaneously disappeared within a month, suggesting nivolumab‐induced immune‐related adverse events.