A carcinoid tumor of the stomach with features of a midgut tumor.

This report is, to our knowledge, the first of a gastric carcinoid tumor that, by electron microscopy, revealed pleomorphic neurosecretory granules similar to those found in carcinoid tumors arising from the midgut. On the basis of silver staining, this lesion would be classified as an argentaffin and argyrophil carcinoid tumor, of the type usually associated with midgut derivation. Immunostaining showed the presence of serotonin granules, and there was clinical evidence of intraoperative hyperserotoninemia. The lesion is believed to have arisen from foci of complete intestinal metaplasia, many of which were present in proximity to the site of the lesion and elsewhere in the stomach.