O 2001 Kluwer Academic Publishers Printed in the Netherlands. Review

Gastroenteropancreatic (GEP) neoplasms originate from any of the various cell types belonging to the neuroendocrine system. A general characteristic of GEP endocrine tumours is that the vast majority produce and secrete a multitude of peptide hormones and amines. Many patients with malignant metastasising tumours present clinical symptoms related to hormone hyperproduction. These include the so-called carci-noid syndrome, characterised by flushing, diarrhoea, wheezing and right heart disease, which is predominantly associated with the serotonin- and tachykinins-producing carcinoids of the midgut. Several types of syndrome associated with GEP endocrine tumors are caused by overproduction of a specific hormone. For instance, the well-known Zollinger-Ellison syn-drome is gastrin-mediated. The so-called 'insulinoma syndrome' depends on excessive production of insulin and proinsulin, resulting in hypoglycemia. The 'glucagonoma syndrome ' is characterised by necrolytic migratory erythema, diabetes and diarrhoea. The Verner-Morrison syndrome, which is brought about by high circulating levels of vasointestinal peptide (VIP), produces severe secretory diarrhoea. Finally the 'somatostati-noma syndrome ' involves gallbladder dysfunction and gall-stones, diarrhoea with or without steatorrhea, and impaired glucose tolerance. The biochemical diagnosis of endocrine digestive tumors is based on general and specific markers. The best general markers are chromogranin A (CgA) and pancreatic polypep-tide (PP). Specific markers for endocrine tumors include in-sulin, gastrin, glucagon, vaso intestinal polypeptide (VIP), somatostatin and the primary cathabolic product of serotonin, 5-hydroxyndoleacetic acid (5-HIAA). Localisation procedures commonly applied, in the diagnosis of endocrine tumours include ultrasound (US), computed tomography (CT) and somatostatin receptor scintigraphy (SRS)