Collision tumor of primary malignant lymphoma and adenocarcinoma in the colon: report of a case.

This report presents the case of a 62-year-old man with a collision tumor of primary malignant lymphoma and adenocarcinoma in the cecum. All regional mesenteric lymph nodes that were removed surgically were found to be occupied by lymphoma cells and no lymph nodes contained any cancer cells, although the primary carcinomas did exhibit lymphatic invasion. Malignant lymphoma was also seen in the duodenum. Systemic chemotherapy was administered for the malignant lymphoma, and a complete response was thus obtained. However, just after chemotherapy multiple liver metastases of adenocarcinoma emerged, and chemotherapy against adenocarcinoma was therefore continued. The occurrence of synchronous lymphoma and adenocarcinoma of the colorectum is rare. Furthermore, collisions of these different entities are also extremely unusual; so far only five such case reports have been published. The accurate clinical determination of the dominant tumor and a close follow-up is required for proper treatment in these cases.