Most gastric carcinoids are enterochromaffin-like (ECL)-cell carcinoids; rarely, other types may occur in the stomach. (Refer to Table 1 in the Cellular and Pathologic Classification of Gastrointestinal Carcinoid Tumors section of this summary for more information.)
Type I ECL-cell gastric carcinoids, the most common type, typically do not have clinical symptoms. They are often discovered during endoscopy for reflux, anemia, or other reasons; and are typically multifocal. Occurring most commonly in women (female-to-male ratio, 2.5:1) at a mean age of 63 years, achlorhydria may be present, and hypergastrinemia or evidence of antral G-cell hyperplasia is usually found.[5,24,27] These tumors are gastrin-driven and arise in a background of chronic atrophic gastritis of the corpus, usually because of autoimmune pernicious anemia but sometimes caused by Helicobacter pylori infection.
Type II ECL-cell carcinoids, the least common type of gastric carcinoids, occur at a mean age of 50 years with no gender predilection. The hypergastrinemia associated with MEN1-Zollinger-Ellison syndrome (ZES) is thought to promote the ECL-cell hyperplasia that leads to type II tumors.[27,28]
Type I and type II ECL-cell gastric carcinoids have been reported to metastasize in fewer than 10% of cases.[27,29] Type III gastric ECL-cell carcinoids, the second most common type of gastric carcinoid, occur mostly in men (male-to-female ratio, 2.8:1) at a mean age of 55 years. There are no neuroendocrine manifestations, and patients typically present with signs and symptoms related to an aggressive tumor.[5,30]
Comprising only 2% to 3% of GI NETs and discovered incidentally or because of symptoms from hormonal or peptide production, duodenal carcinoids may also arise in the periampullary region, obstruct the ampulla of Vater, and produce jaundice.[3,5,31] The age at presentation varies widely (range, 19–90 years; mean age, 53 years).[15,32]
The most common duodenal carcinoids are gastrin-producing G-cell tumors (~two-thirds) followed by somatostatin-producing D-cell tumors (~one- fifth), which rarely produce systemic manifestations of somatostatin excess.[5,31,33]
Gastrin production from G-cell carcinoids (also called gastrinomas if serum gastrin levels are elevated) results in ZES in approximately one-third of the cases of duodenal G-cell tumors. Although duodenal G-cell carcinoids may occur sporadically, 90% of patients with MEN1 develop them. The clinical manifestations of serum gastrin elevation include:
- Abdominal pain.
- Hemorrhage from multiple and recurrent peptic ulcers.
- Gastroesophageal reflux caused by excess acid production.
- Diarrhea from hypergastrinemia.