ABSTRACT
Gastric mixed adenoneuroendocrine carcinoma (MANEC) is an entity defined by World Health Organization in 2010, which is composed of adenocarcinoma and neuroendocrine neoplasm. This is a very rare type of tumor in the stomach, which is estimated to be one to two per one million people per year on gastrointestinal track. In general, as MANEC often shows a poor prognosis, early diagnosis of the disease is important for achieving a favorable outcome. However, due to its rarity and histological heterogeneity, it is hard to suspect this disease initially, and sometimes this tumor is misdiagnosed as adenocarcinoma. The present case was a 76-year-old man who was initially diagnosed with gastric tubular adenocarcinoma without distant metastasis. Only 1 month after a curative surgery, multiple liver metastases were newly detected. Retrospective pathologic review resulted in a revised diagnosis as a gastric MANEC, and the patient underwent palliative systemic chemotherapy to achieve partial response.