A case of gastric mixed adenoneuroendocrine carcinoma with difficulty in diagnosis before endoscopic submucosal dissection.

A woman in her 60s was referred to our hospital with a superficial depressed lesion measuring 8mm in diameter on the lesser curvature of the lower gastric body. Initial biopsy of the lesion indicated a moderately differentiated adenocarcinoma. Endoscopic submucosal dissection was performed, and pathological examination revealed a tumor comprised of adenocarcinoma and neuroendocrine carcinoma with submucosal infiltration, with the final pathological diagnosis being gastric mixed adenoneuroendocrine carcinoma (MANEC). Laparoscopic gastrectomy was subsequently performed. No recurrence was observed after 18 months. Most neuroendocrine carcinomas including MANEC are diagnosed at an advanced stage and require surgical resection. Here we report a case of gastric MANEC mimicking early gastric cancer that was removed en bloc via endoscopic submucosal dissection.