Gastric collision tumor: Case report of a rare adenocarcinoma and a typical carcinoid tumor

We report a case with features of gastric adenocarcinoma colliding with a typical carcinoid component. A 51-year-old female was admitted to the Department of Internal Medicine with complaints of epigastric pain. On physical examination of the patient there was significant epigastric tenderness and the CA19-9 level was higher than the normal titer value. An upper gastrointestinal endoscopy showed an ulcerated polypoid mass located on the cardiac region of the stomach. Pathological and immunohistochemical findings diagnosed as a collision tumor comprising both adenocarcinoma and carcinoid tumor. Metastasis of adenocarcinoma was found in 7 perigastric lymph nodes, while metastasis of the carcinoid was not detected. The admixture of neoplastic endocrine and nonendocrine cells, have been found infrequently in gastric tumors. The mixed tumors can be further classified into composite tumors that show an admixture of two histological components with histological transitions and collision tumors where the two components are not intermixed In general it is not easy to morphologically distinguish a collision tumor, from composite tumor. Microscopically, hematoxylin and eosin-stained tissue sections from two different areas of the mass revealed two different types of tumor; an intestinal type adenocarcinoma and a carcinoid tumor. We report a case with features of adenocarcinoma colliding with a typical carcinoid component, along with a review of the literature.