Objective To determine the value of colonoscopy in the diagnosis and treatment of patients with immune checkpoint inhibitor-induced colitis.

Methods Patients who developed colitis and underwent colonoscopy after receiving immune checkpoint inhibitors (ICIs) therapy at Tianjin Medical University General Hospital between December 2020 and December 2023 were reviewed, according to the guidelines of the Chinese Society of Clinical Oncology for the management of ICI-related toxicity. The effect of the treatment and the relationship between prognosis and the pathological features of colonoscopy were analyzed.

Results Patients with ICI-associated colitis who underwent colonoscopy had a more than 3 degrees diarrhea, and diffused inflammatory features such as mucosal erythema, exudate, erosion, loss of vascular markings, and edema were observed under the microscope, and the presence of ulcers greater than 1 cm in diameter and/or more than 2 mm deep indicate a poor prognosis for enteritis. Histopathological studies showed changes in glandular structures, such as cryptitis and crypt abscess. The pathological colonoscopic manifestations of patients with microscopic enteritis were inconsistent, and more deep samples should have been taken.

Conclusions The toxicity grading of ICI-associated colitis is not limited to clinical manifestations, but refers to the multi-dimensional analysis of colonoscopic features and histopathological characteristics. Soft colonoscopy can be used as an important follow-up method for patients with colitis, owing to its ease of operation and good tolerance.