Severe colitis induced by pembrolizumab in a patient with advanced hypopharyngeal squamous cell carcinoma: A case report of an immune-related adverse event

Immune checkpoint inhibitors (ICIs) are monoclonal antibodies that target downregulators of anticancer immune responses: cytotoxic T-lymphocyte antigen-4 (CTLA-4), programmed death protein-1 (PD-1) and programmed death-ligand 1 (PD-L1). Immune-related adverse events (irAEs) can affect multiple organs of the body. Distinct toxicity induced by different ICIs had been observed. Immune-mediated colitis (IMC) is a common irAE and more frequently encountered in anti-CTLA-4 than anti-PD-1 or anti-PD-L1. Owing to a wide range and inconclusive endoscopic and histological findings, the diagnosis of IMC can be made after excluding other possible causes and relies primarily on clinical suspicion. Optimal management of IMC requires early recognition and timely treatment. Corticosteroids are recommended for Grade 2 or more severe colitis while holding the immunotherapy. A better response to corticosteroids has been observed in anti-PD-1-related IMC than in anti-CTLA-4. Herein, we report a case of severe colitis induced by pembrolizumab.