A Gastric Intramucosal Mixed Adenocarcinoma-Neuroendocrine Tumor.

Gastric mixed adenocarcinoma-neuroendocrine tumor (NET) is a rare composite tumor, and a limited number of studies have reported on it. A 77-year-old man was admitted to our hospital because of acute cholecystitis. He underwent a cholecystectomy. Esophagogastroduodenoscopy during his admission revealed a slightly elevated tumor, and biopsy demonstrated a well-differentiated tubular adenocarcinoma. The tumor was resected completely by endoscopic submucosal dissection. Histological findings showed that it measured 9 mm in diameter, was located within the mucosa, and consisted of well-differentiated tubular adenocarcinoma and a NET G1. The NET was covered with adenocarcinoma and both components exhibited histological continuity. The NET and a part of the adenocarcinoma component showed a positive reaction for chromogranin A and synaptophysin. Neither enterochromaffin-like cell hyperplasia nor endocrine cell micronest surrounded the tumor. The diagnosis was gastric mixed adenocarcinoma-NET. The histological continuity between the two components can be likened to the same histogenesis.