A unique early gastric tubular adenocarcinoma arising from a pre-existent carcinoid tumor in a patient with a more than 20-year history of type A gastritis: an immunohistochemical and ultrastructural study.

A unique early gastric tubular adenocarcinoma developed from a pre-existent carcinoid tumor in a patient with a more than 20-year history of type A gastritis, multiple endocrine cell micronests, hypergastrinemia, and a high level of serum antiparietal cell autoantibody. The patient was a 60-year-old Japanese man. The background gastric mucosa around the tumor showed marked atrophy with intestinal metaplasia, in which endocrine cell micronests were frequently observed, and was consistent with type A gastritis. The mass was composed of both adenocarcinoma and carcinoid tumor. The adenocarcinoma was restricted to the lamina mucosa and submucosal area, and constituted a minor component of the tumor mass. The carcinoid tumor was the dominant constituent of the tumor, that invaded continuously the subserosa and muscularis propria. Based on this examination together with the detailed immunohistochemical and ultrastructural studies, the adenocarcinoma was presumed to have developed from the pre-existent carcinoid tumor. Ultrastructurally there were no amphicrine cells in the tumor, containing both endocrine granules and mucin droplets.