Pancreatic endocrine tumors arise from the pancreatic islets. Pancreatic islets are composed of a variety of cells with different functions, and pancreatic endocrine tumors with different cellular origins present with different clinical syndromes. Functional endocrine tumors are named according to the main hormone they produce. Tumors with normal serum hormone levels and no clinical symptoms are called nonfunctional pancreatic endocrine tumors. All pancreatic endocrine tumors appear similar under light microscopy and are difficult to distinguish on routine histological examination. Immunofluorescence technique and peroxidase-antiperoxidase technique can reveal specific hormones within the tumor cells and facilitate the diagnosis. Whether it is malignant is determined by the presence or absence of local infiltration, regional lymph nodes, liver or distant metastases. Classification of functional pancreatic endocrine tumors Tumor name Major hormone Cell type Symptoms Malignancy rate Located outside the pancreas Insulinoma Insulin B Hypoglycemia 15% Rare Gastrinoma Gastrin G Pancreatic-derived ulcer (Zollinger-Elli son syndrome), diarrhea 50% Common Enteropeptidoma VIP, prostaglandin D1 Watery diarrhea, low potassium, low gastric acid (Verner- Morrison syndrome) 90% Occasionally Morrison syndrome 90% Occasionally Hyperglycemia Hyperglycemia A Hyperglycemia, dermatitis 60% Rare Growth suppressor tumor Growth suppressor D Hyperglycemia, steatorrhea, gallstones 90% Rare