Synchronous lymphoma and adenocarcinoma occurring as a collision tumor in the stomach: report of a case.

We report herein the rare case of a 71-year-old man who was initially operated on under the diagnosis of advanced gastric cancer, but was subsequently found to have synchronous lymphoma and early adenocarcinoma of the stomach, confirmed by postoperative pathological examination. The patient had a history of lymphoma of the left tonsil, and histologically the gastric lymphoma was observed to be of the non-Hodgkin's, diffuse, large-cell type. Conversely, the gastric cancer was early well-differentiated tubular adenocarcinoma of type 0-IIa, according to the Japan Gastroenterological Endoscopy Society classification. The two tumors had collided at the fornix. The relationship between these two tumors is analyzed and the most appropriate methods of diagnosis and treatment are discussed.