A somatostatinoma is a tumour that produces somatostatin. 50% are found in the pancreas with the remainder in the duodenum, the jejunum and the biliary tree. The majority (90%) are malignant, arising from the delta cells in the Islets of Langerhans.
Somatostatinomas are extremely rare, with an estimated incidence of 1 in 40 million. Only 50 have been reported to date. Over five types of somatostatin may be secreted from the tumour, each type producing different symptoms.