A Case of Gastric Mixed Neuroendocrine-Nonneuroendocrine Neoplasm Composed With Adenoma and Neuroendocrine Tumor.

Mixed neuroendocrine-nonneuroendocrine neoplasms (MiNENs) of the gastrointestinal tract, particularly gastric MiNENs are rare, and a gastric adenoma that occurs concomitant with a neuroendocrine carcinoma (and not gastric adenocarcinoma) is extremely rare. The clinicopathologic and pathogenetic features of MiNENs remain unclear, and treatment guidelines are currently unavailable. A 75-year-old man patient was referred to our hospital for management of a gastric adenoma. Endoscopy revealed an elevated mucosal lesion (10 mm×10 mm) at the greater curvature of the lower gastric body. The patient underwent endoscopic submucosal dissection for removal of the gastric neoplasm. Histopathological evaluation revealed mixed epithelial dysplasia, low and partly high grade and a neuroendocrine tumor (grade 1). Immunohistochemical analysis showed neoplastic cells with immunopositivity for CD56, synaptophysin, and INSM1, and Ki-67 showed 2.2%. Therefore, the patient was diagnosed with a low-grade gastric MiNEN. We present a rare case of gastric MiNENs (adenoma-neuroendocrine tumor) together with a literature review.