Early gastric mixed neuroendocrine‐non‐neuroendocrine neoplasm with early poor prognosis after endoscopic submucosal dissection: A case report

Early gastric mixed neuroendocrine‐non‐neuroendocrine neoplasms (MiNENs) are rare diseases, with no data on their incidence and prognosis. We report the case of intramucosal gastric MiNENs for endoscopic submucosal dissection (ESD) treatment. An 80‐year‐old male underwent esophagogastroduodenoscopy for screening and was suspected of early gastric cancer type 0‐IIa+IIc on the lesser curvature of the antrum, for which ESD treatment was performed. Histopathologically, the diagnosis was MiNENs. Synaptophysin‐positive adenoductal structures were observed in the adenocarcinoma component, suggesting that adenocarcinoma had dedifferentiated into neuroendocrine carcinoma. The tumor was located within the mucosal layer, with lympho‐vascular invasion. The patient was kept under observation; however, 6 months after the ESD, computed tomography scan revealed prominent ascites, enlarged lymph nodes, and liver metastases, and MiNENs were suspected to have poor prognosis. If MiNENs diagnosis is made preoperatively or postoperatively, surgical resection may be considered as treatment regardless of the tumor depth or lympho‐vascular invasion.