PPY and gastrin-producing neuroendocrine tumor: By the age of 40, the prevalence of gastrinoma is 30–40%, that of insulinoma is 10%, and that of other functioning pNETs such as glucagonoma, VIPoma, somatostatinoma, etc. is 2%, whereas the prevalence of non-functioning enteropancreatic tumors including those that secrete pancreatic polypeptide is 20–55% (5).