Carcinoid Tumor of the Stomach

Abstract

Gastric carcinoid tumors (in fact, carcinoid tumors of the gastrointestinal [GI] tract in general) have undergone a dizzying array of name changes over the years, reflecting their ability to behave aggressively while appearing rather banal. Thus, a tumor with bland morphology can invade vascular structures and metastasize to lymph nodes or liver. While generally categorized as “neuroendocrine” tumors (NET), they have been classified by some observers as “well-differentiated neuroendocrine tumors,” “well-differentiated neuroendocrine carcinomas,” and so on. Bona fide small-cell carcinomas and large-cell neuroendocrine carcinomas can occur in the stomach, but they are rare. Thus, we will concentrate on the most frequently encountered entities here, which—even after all of the arguing about nomenclature—are still commonly called gastric “carcinoids.” Most such tumors in the stomach consist of enterochromaffin-like (ECL) cells that have been induced to undergo hyperplasia/proliferation by a hypergastrinemic state. To sort out the variety of situations in which these tumors occur, they have been categorized into several types. “Type 1” tumors arise in the setting of ECL cell hyperplasia brought on by autoimmune atrophic gastritis (AAG; see Chap. 20) and account for the vast majority of gastric carcinoids. “Type 2” tumors arise in the setting of Zollinger-Ellison syndrome (ZES; also in Chap. 20), and usually occur when this condition is associated with multiple endocrine neoplasia type 1 (MEN-1). “Type 3” (“sporadic”) gastric carcinoids are thought to arise from true enterochromaffin cells (ECC) and are often larger and more aggressive than the ECL cell-derived tumors. Finally, some patients with defective parietal cell acid-secreting machinery unrelated to AAG or ZES have hypergastrinemia and can develop ECL cell-derived carcinoid tumors designated “Type 4.” Types 1, 2, and 4 (the ECL cell tumors) arise in the gastric body/fundus, whereas type 3 tumors can arise anywhere in the stomach. The ECL cell-derived tumors also have a good prognosis, compared to type 3 tumors.