Pembrolizumab-induced Focal Pancreatitis Diagnosed by Endoscopic Ultrasound-guided Fine-needle Aspiration.

A 69-year-old man with advanced non-small-cell lung cancer was treated with pembrolizumab for 4 months. Three months after pembrolizumab was discontinued, computed tomography showed enlargement of the pancreatic head, with hypoattenuating areas in the pancreatic head to body. On endoscopic ultrasonography, the entire pancreatic parenchyma was hypoechoic. Endoscopic retrograde cholangiopancreatography showed narrowing of the main pancreatic duct at the pancreatic head. Endoscopic ultrasound-guided fine-needle aspiration showed inflammatory cell infiltration in the stroma but no neoplastic lesions. CD8-positve T cells were dominant over CD4-positive T cells in the infiltrating lymphocytes, and the patient was diagnosed with pembrolizumab-induced pancreatitis.