Gastrointestinal Adverse Events Induced by Immune-Checkpoint Inhibitors

Background: As immune-checkpoint inhibitors (ICI) are becoming standard therapies for malignant tumors, increasing attention has been paid to their associated immune-related adverse events (irAEs). The gastrointestinal tract is the major site of irAEs, and it has recently become evident that the large bowel is the most frequently affected region. The aim of this narrative review was to clarify the endoscopic and histopathologic findings of and treatments for ICI-induced colitis.

Summary: Endoscopic findings of ICI-induced colitis include a reddish, edematous mucosa with increased mucous exudate, loss of normal vascularity, and a granular mucosa with or without mucosal breaks. Histopathologic findings of ICI-induced colitis are expansion of the lamina propria, intraepithelial infiltration of neutrophils, crypt architectural distortion, neutrophilic crypt abscess, and prominent apoptosis. The clinical, endoscopic, and histopathologic severity of ICI-induced colitis is diverse, but colonoscopy together with biopsy is necessary for diagnosis. While a certain proportion of patients with ICI-induced colitis have an intractable clinical course, management guidelines are based on retrospective analyses. Prospective studies are needed to assess the efficacy of various medications, including immunosuppressive regimens. Key Messages: Colonoscopy with biopsy is the gold standard for the diagnosis of ICI-induced colitis. Endoscopists should be aware of the clinical features and pathophysiology of ICI-induced colitis for prompt diagnosis and treatment planning.