Isolated immune-related pancreatic exocrine insufficiency associated with pembrolizumab therapy

We report a case of isolated immune-related pancreatic exocrine insufficiency in a patient treated with pembrolizumab for metastatic melanoma. This patient presented with explosive diarrhea and was treated with high dose corticosteroids for possible immune-related colitis. However, biopsies from colon and duodenum did not show any histological evidence of colitis/enteritis. Serum amylase and lipase were not elevated. There was no evidence of pancreatitis or pancreatic metastases on imaging. Significantly lower fecal elastase test on two occasions confirmed the diagnosis of pancreatic exocrine insufficiency. He was treated with pancreatic enzyme supplementation with complete resolution of diarrhea. This case reinforces the importance of awareness and anticipation of unusual immune-related adverse events related to checkpoint inhibitors.