A Case of a Collision Cancer Composed of Gastric Adenocarcinoma and Neuroendocrine Carcinoma with a Submucosal Tumor-like Morphology

Abstract

A 74-year-old woman presented to our hospital for close examination of a gradually enlarging gastric submucosal tumor which had been pointed out elsewhere 5 years previously. An esophagogastroduodenoscopy revealed a 20-mm submucosal tumor-like lesion associating with a shallow ulcer at its top in the greater curvature of the pyloric antral zone. The lesion was diagnosed as gastric adenocarcinoma by a biopsy. Using endoscopic ultrasonography, it was diagnosed as submucosal carcinoma mainly located in the third layer. There were no lymph node nor distant metastases. We thus performed laparoscopic distal gastrectomy with the diagnosis of cT1b, cN0, cM0 and cStage I. Histopathology confirmed about 80 % of atypical cells to be composed of adenocarcinoma component and about 20%, neuroendocrine carcinoma component. We diagnosed the case as collision tumor composed of adenocarcinoma and neuroendocrine carcinoma, pT1b2, pN0. She has been alive without recurrence, as of 16 months after the operation. This is the first case report of collision tumor with a gastric submucosal tumor-like morphology in Japan. In treating submucosal tumor-like gastric cancer, we should carefully diagnose and treat it by keeping a possible existence of collision tumor in mind.