Delayed-Onset Immune-Related Colitis Following Pancreaticoduodenectomy in Patients With Gastric Cancer and Pancreatic Invasion Treated With Immune Checkpoint Inhibitors.

Immune checkpoint inhibitors (ICIs) have been approved for treating various advanced malignancies. Immune-related adverse events (irAEs) can manifest diversely and at varying times. However, postoperative diarrhea is a common complication in pancreaticoduodenectomy (PD). This case report presents a unique instance of delayed-onset irAE colitis occurring one year after PD in a patient with gastric cancer who received neoadjuvant nivolumab, a monoclonal antibody targeting human programmed death 1. A 54-year-old male developed severe diarrhea and weight loss, ultimately diagnosed with irAE colitis, which responded to steroid therapy. This report underscores the importance of extended monitoring, recognizing the potential for late-onset toxicities associated with ICIs, and differentiating from PD-related diarrhea.