Simultaneous large cell neuroendocrine carcinoma and adenocarcinoma of the stomach.

A large cell neuroendocrine carcinoma (LCNEC) of the stomach is very rare. A 76-year-old Japanese man was admitted to our hospital because of epigastralgia and nausea. Endoscopy revealed 2 large tumors in the stomach. He did not have multiple endocrine neoplasia type I or Zollinger-Ellison syndrome. Imaging modalities, including computed tomography and magnetic resonance imaging, revealed no other tumors. Gastrectomy, cholecystectomy, and lymph node dissection were performed. The resected stomach had 2 tumors: one was an antral ulcerated type 3 tumor measuring 5 cm x 5 cm, and the other was a polypoid type 1 tumor measuring 6 cm x 6 cm x 3 cm in the fundus. Microscopically, the antral ulcerated tumor was a well differentiated adenocarcinoma with deep invasion. The fundus polypoid tumor was a LCNEC, being composed of malignant large cells arranged in trabecular and nested patterns. The tumor cells were large and the nuclei were vesicular. Nucleoli were frequently present, and there were many mitotic figures, apoptotic bodies, and necrotic areas. Much lymphovascular permeation was seen. Seven out of 29 dissected lymph nodes showed metastatic foci; 6 were from the LCNEC and 1 from the adenocarcinoma. Many intravascular tumor emboli of LCNEC were seen in the peritoneum around the lymph nodes. Mucins were present in the adenocarcinoma but not in the LCNEC. Immunohistochemically, the LCNEC tumor cells were positive for pancytokeratins, synaptophysin (50% positive), chromogranin A (10% positive), Ki-67 (90% labeled), and platelet-derived growth factor-α (80% positive). They were negative for KIT, p53, CD56, and neuron-specific enolase. The non-cancerous stomach showed a normal number of endocrine cells. The patient is now treated with adjuvant chemotherapy.