Abstract
Immune checkpoint inhibitors (ICIs) are important immunotherapeutic tools with known potential for adverse events (immune-related adverse events [irAEs]) in the gastrointestinal system. Although ICI-induced colitis and diarrhea are well documented, irAEs localized to the stomach are less frequently described. The management of most irAEs is suspension of ICI therapy and immune suppression. In rare cases of ICI-induced gastritis, treatment strategies of immune suppression have been scarcely described. To our knowledge, there have been no reported cases of severe ICI-induced gastritis leading to fistula formation. This case report describes a patient with isolated ICI-induced gastritis leading to an ulcer with gastrocolic fistula and his treatment course.