Ulcerative colitis exacerbation after the onset of immune checkpoint inhibitor related colitis

Immune checkpoint inhibitors (ICPI) have been reported to be effective in various carcinomas. They excessively activate the immune system, resulting in frequent immune-related adverse events (irAEs). Colitis induced by ICPI is one of the most common and is known as immune-mediated colitis (IMC). Although IMC and inflammatory bowel disease (IBD) are similar in many respects, there are very few reports of IMC in patients with preexisting IBD such as ulcerative colitis (UC) and Crohn's disease (CD). Whether preexisting IBD is concerned with the development of the colitis is not well known. Here, we reported the case who developed severe ulcerative colitis which started from IMC. It is an important case to follow the time course of the colitis developed. Our conclusion indicated that frequent colonoscopy was important for the management of IMC in a patient who has suffered chronic inflammatory disease, such as UC.