Collision tumor of the stomach: a rare case of an adenocarcinoma and carcinoid tumor.

We report a rare case of gastric collision tumor composed of moderately differentiated tubular adenocarcinoma and carcinoid in an 84-year-old woman. On endoscopic examination, an invasive tumor was noted at the cardia of the stomach, and a pathologic examination of the biopsy specimen revealed adenocarcinoma. After total gastrectomy, a thorough histopathologic examination of the resected tumor revealed the concurrent presence of moderately differentiated adenocarcinoma and a typical carcinoid tumor, which had a colliding pattern of tissue proliferation. There was no intermixing or transition area between the 2 components. The final pathologic diagnosis was collision tumor of the adenocarcinoma and carcinoid tumor. The presence of either tumor individually would not be especially noteworthy, but this collision-type tumor of both histopathologic types in the stomach is, to our knowledge, only the sixth such case in the literature.