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Esophageal neuroendocrine neoplasms are extremely rare, and their prognosis is poor. Mixed neuroendocrine non-neuroendocrine neoplasms (MiNENs) are even more rare and are defined as tumors consisting of neuroendocrine carcinoma and either adenocarcinoma or squamous cell carcinoma. We report a rare case featuring endoscopic submucosal dissection (ESD) for an esophageal MiNEN, arising from the ectopic gastric mucosa in the lower thoracic esophagus. A 92-year-old male patient was referred to this hospital for investigation of an esophageal tumor. An endoscopic examination revealed a 10 mm elevated lesion, with 8 mm flat areas on the anal side, within the ectopic gastric mucosa located in the lower thoracic esophagus. ESD was carried out, and a histopathological examination revealed a tubular adenocarcinoma composed of differentiated neuroendocrine cells. Immunohistochemical staining was positive for synaptophysin and negative for chromogranin A. The labeling index of Ki-67 was more than 80%. Based on these results, we diagnosed the lesion as an esophageal MiNEN, arising in the ectopic gastric mucosa of the esophagus. The patient remains alive, without recurrence of cancer, 24 months after ESD.