From Innovation to Complication: A Case Report and Review on Immune-Related Colitis Induced by ICIs.

Immune checkpoint inhibitors (ICIs) have revolutionized cancer therapy by providing durable responses and a favorable safety profile, ushering in a new era of tumor immunotherapy. However, immune-related adverse events (irAEs) remain a significant clinical challenge. Among these, gastrointestinal irAEs, especially immune-related colitis (ir-colitis), can lead to serious complications if not promptly recognized and managed. Here, we present a case of grade 3 ir-colitis induced by the programmed cell death protein 1 (PD-1) inhibitor sintilimab in a 68-year-old woman with endometrial cancer. The patient developed severe acute diarrhea following ICI administration, which progressed despite initial antidiarrheal and antimicrobial treatments. A multidisciplinary team (MDT) involving gastroenterologists, oncologists, a pathologist, and a clinical pharmacist confirmed the diagnosis and implemented high-dose corticosteroid therapy, yielding significant clinical improvement. Importantly, this report highlights the mechanistic link between PD-1 blockade and ir-colitis pathogenesis, focusing on the dysregulation of the mucosal immune environment and its role in triggering colonic injury. In addition to the case description, we provide a comprehensive review of the literature and clinical guidelines, discussing risk factors, diagnostic approaches, therapeutic strategies, and long-term monitoring. By integrating insights from pharmacology, immunology, and clinical practice, this work emphasizes the importance of early detection, patient education, and MDT collaboration for optimizing therapeutic outcomes and advancing the understanding of ir-colitis in the context of ICI therapy.