A resected case of neuroendocrine carcinoma of the stomach with unusual lymph node metastasis.

Gastric endocrine cell carcinoma is a relatively rare tumor. We experienced a case of early gastric cancer in which an endocrine cell carcinoma was identified within a differentiated adenocarcinoma, and a component of this endocrine cell carcinoma had metastasized to lymph nodes of the stomach. In its 2010 revision regarding digestive system tumors, WHO classified cancer cells with characteristics of both glandular system cells and neuroendocrine cells as mixed adeno neuroendocrine carcinoma (MANEC) under the neuroendocrine carcinoma (NEC) category. In this case, we observed an endocrine cell carcinoma continuous with an intramucosal differentiated adenocarcinoma, and cancer cells with an irregular gland duct structure were observed in the proliferative portion of the submucosal tissue. In addition, there was a 35 mm size lymph node metastasis in the lesser curvature of the stomach consisting entirely of poorly differentiated cancer cells with polymorphic, highly atypical nuclei and scant cytoplasm. Immunohistological analysis showed that the endocrine carcinoma in the gastric mucosa was chromogranin A positive and the infiltrated area of the submucosal tissue was also chromogranin A positive. The lymph node metastasis was positive not only for chromogranin A, but also for Synaptophysin and CD56. Furthermore, the Ki67 labeling index was high at approximately 80 % for the gastric endocrine cell carcinoma and approximately 90 % for the lymph node metastases. Until now, there are no reports related to the patients with early gastric cancer accompanied with lymph node metastasis of MANEC. This case is very interested in considering the mechanism of lymph node metastasis of MANEC. The patient has shown no sign of recurrence for 1 year and 4 months after postoperative chemotherapy.