Pembrolizumab-Induced Duodenitis Mimicking Celiac Disease.

Pembrolizumab is a programmed cell death-1 (PD-1) inhibitor frequently used as primary immunotherapy in many cancers, including melanoma, lung, renal cell, cervical, urothelial, and gastric cancers. Given its immune-checkpoint inhibition and upregulation of the immune response, pembrolizumab has been associated with many immune system-related adverse effects including stomatitis, conjunctivitis, pneumonitis, myositis, and even type 1 diabetes mellitus. Colitis is the most frequent gastrointestinal adverse reaction, with upper gastrointestinal reactions like esophagitis, gastritis, and duodenitis being rare. In this report, we present a case of pembrolizumab-induced enteropathy that endoscopically and histologically mimicked celiac disease.