A rare cancer that forms in islet cells (hormone-making cells) of the pancreas. Islet cells make several different hormones that affect body functions, including controlling the amount of glucose (sugar) in the blood and helping digest food in the stomach. Functional islet cell carcinomas make extra amounts of these hormones, which can cause symptoms. Nonfunctional islet cell carcinomas do not make extra amounts of hormones, but they may cause symptoms as they grow and spread. Also called pancreatic endocrine cancer.