[Rectal tumor differentiating into neuroendocrine lineage:a case report].

A 79-year-old woman underwent colonoscopy that revealed a 30-mm-sized nodular, mixed-type, lateral spreading tumor-granular in the lower rectum. Endoscopic submucosal dissection was performed, and the pathological findings indicated a mostly adenoma-type tumor with synaptophysin, cluster of differentiation 56-positive, and chromogranin A-negative associated with neuroendocrine carcinoma. Surgical resection was performed owing to vascular invasion, and the lymph node metastasis of the endocrine carcinoma component was observed. Thus, we reported a rare case of the coexistence of adenoma and neuroendocrine carcinoma.