Advanced Gastric Neuroendocrine Carcinoma with an Adenocarcinoma Component

In the present study, we observed that the adenocarcinoma component in the mucosa was continuous with neuroendocrine carcinoma (NEC) in the deeper layers; this suggests the normal course of NEC carcinogenesis at the histological level. A 72-year-old man was admitted to our hospital with a chief complaint of tarry stools. Endoscopic examination of the upper gastrointestinal tract revealed a 2-cm tumor, with a deep central depression, surrounded by a smooth elevated area, in the middle of the stomach body. A biopsy showed that the tumor was a moderately differentiated gastric adenocarcinoma. The patient underwent total gastrectomy and standard lymph node dissection. The resected tumor was a 3.5 × 2.5 cm type 2 lesion. It comprised two elements at the histological level: (i) a moderately differentiated adenocarcinoma in the superficial portion of the mucous membrane layer, and (ii) NEC-like cells with dark, round nuclei and scant cytoplasm, presenting a solid and trabecular pattern, in the submucosal and muscularis propria layers. Immunohistochemical findings showed that the NEC-like cells were diffusely positive for chromogranin A, synaptophysin, neural cell adhesion molecule, and neuron-specific enolase, but were negative for carcinoembryonic antigen. The Ki-67 labeling index was 95%. The final pathological diagnosis was gastric NEC with an adenocarcinoma component and a high cellular proliferative potential.