Gastric carcinoid tumors: Distinction among types, and why evaluation of the background gastric mucosa really matters

The incidence of endocrine tumors of the stomach is increasing. Most gastric endocrine tumors are well-differentiated neoplasms of enterochromaffin-like cells, the major endocrine cell type of the gastric body and fundus. These gastric carcinoids (GCs) show relatively uniform cells with a low (<2/10 high-power fields) mitotic rate and no necrosis. Poorly-differentiated neuroendocrine carcinomas (large and small cell) are much less common and are characterized by high (>10/10 high-power fields) mitotic rate, frequent necrosis, and poor prognosis as compared with both GCs and to conventional gastric adenocarcinomas. GCs are subdivided into 3 major types with different clinical associations, management, and prognosis. Type I (autoimmune gastritis-associated) are the most common; they tend to be small, lack muscularis propria invasion, have low rates of lymph node and distant metastases, and only rarely are lethal. Type II (Zollinger-Ellison syndrome-associated, especially as part of multiple endocrine type-1) are the least common; their mean size, depth of invasion, and metastatic rate are intermediate between type I and type III GCs, yet even metastatic tumors do not usually result in death. Both types I and II arise in a background of enterochromaffin-like cell hyperplasia-dysplasia due to the trophic effects of hypergastrinemia, and therefore, are frequently multifocal and confined to the gastric body and fundus. Type III (sporadic) GCs are independent of gastrin and are therefore solitary tumors that can arise throughout the stomach. They are frequently large, deeply invasive, have high rates of lymph node and liver metastases, and approximately one-fourth are lethal. A fourth type of GC may exist in patients with hypergastrinemia because of congenital or acquired defects in acid secretion from parietal cells. Separation of sporadic GCs from other types is important because the former are treated surgically with a cancer operation, whereas the latter are generally managed more conservatively.