[Colitis Suggested to be Related to Nivolumab in a Gastric Cancer Patient with a History of Ulcerative Colitis: A Case Report].

We experienced a case in which long-term use of nivolumab in a patient with a history of ulcerative colitis led to disease control of gastric cancer. The case is a 77-year-old man. The patient had a history of ulcerative colitis and remained in remission on mesalazine 1500 mg/d. With continuous monitoring, nivolumab could be continued up to 16 courses, but was withdrawn due to the appearance of diarrhea (grade 1) and bloody stools, which was relieved with prednisolone (PSL) 40 mg/d. After two more courses, diarrhea (grade 3) appeared again, which improved with PSL 60 mg/d and increased dose of mesalazine. It is difficult to distinguish whether colitis that occurs after nivolumab administration is due to relapse exacerbation or irAE. The onset of irAE colitis is often reported within 3 months, and the fact that this patient developed irAE colitis after 8 months, despite having ulcerative colitis, is considered novel. In the future, we hope to accumulate cases so that immune checkpoint inhibitors can be used safely in patients with ulcerative colitis, and to establish appropriate methods for their use.