Gastric carcinoid tumors: the biology and therapy of an enigmatic and controversial lesion.

Gastric carcinoid tumors were previously believed to be rare lesions, representing less than 2% of all carcinoid tumors and less than 1% of all stomach neoplasms. More recent studies have demonstrated that they may constitute as much as 10-30% of carcinoid tumors. Patients with conditions associated with hypergastrinemia, such as chronic atrophic gastritis, Zollinger-Ellison syndrome with multiple endocrine neoplasia type 1 (ZES-MEN-1), and pernicious anemia, display a markedly elevated incidence of gastric carcinoid tumor formation. A classification system distinguishing three types of gastric carcinoid tumor has been proposed: 1) tumors associated with chronic atrophic gastritis, 2) tumors associated with Zollinger-Ellison syndrome, and 3) sporadic lesions. Tumors that develop in association with hypergastrinemia are usually composed of enterochromaffin-like (ECL) cells, in contrast to sporadic lesions that contain a variety of endocrine cell types (enterochromaffin, ECL, X). In both intact animal models such as the rat and Praomys (mastomys) natalensis and in isolated purified ECL cell preparations, gastrin has been demonstrated to exert a powerful trophic effect on ECL cells, in addition to stimulating histamine secretion. It is apparent that hypergastrinemia-associated gastric carcinoids display relatively benign biological behavior. Sporadic lesions require aggressive surgical management on diagnosis. Type I and type II (hypergastrinemia-associated) lesions can be managed initially by endoscopic excision of accessible tumors, followed by endoscopic surveillance. If tumors recur, antrectomy and local excision may be used to remove the source gastrin, resulting in cure in the vast majority of patients.