Simultaneous adenocarcinoma and leiomyoma of the stomach presenting as a collision tumor.

A 68-year old Japanese man was referred to the Cancer Institute Hospital for the treatment of a rectal cancer. Preoperative esophagogastroduodenoscopy revealed a submucosal tumor with ulcer formation near the esophagogastric junction of the stomach. The initial treatment strategy was to perform a proximal gastrectomy with limited lymph node dissection as well as a simultaneous anterior resection. However, histopathological examination of a biopsy specimen of the submucosal tumor revealed a moderately differentiated adenocarcinoma, and therefore a total gastrectomy with D2 lymph node dissection was performed. Histopathological examination of the resected specimen revealed both adenocarcinoma and leiomyoma presenting as a collision tumor. Preoperative accurate histopathological diagnosis of a gastric submucosal tumor is generally difficult. Consequently, surgical resection of large gastric submucosal tumors may be indicated in the absence of histopathological confirmation of the diagnosis. However, in this case preoperative histopathological diagnosis enabled surgeons to perform the appropriate surgery. We conclude that to determine the appropriate treatment strategy, preoperative histopathological examination of tumors should be performed even in a case of suspected submucosal tumor, particularly if mucosal ulceration is present.