A case of mixed adenoneuroendocrine carcinoma of the common bile duct: initially diagnosed as cholangiocarcinoma.

Neuroendocrine tumors (NETs) are mostly found in the gastrointestinal tract and the pancreas. The World Health Organization (WHO) classification (2010) has been widely used to categorize NETs [1]. In the digestive system, NETs including those found within the bile ducts, are classed as NET G1 (carcinoid, mitotic count of 20 per 10 HPF and/or >20% Ki-67 index), and mixed adenoneuroendocrine carcinoma (MANEC) [1]. NETs arising from the bile duct are rare, accounting for only 1.8% of gastroenteropancreatic NETs [2]. MANECs of the common bile ducts (CBDs) are extremely rare, and only a few cases have been reported thus far [3-5]. In this study, we report a case of MANEC arising from the mid CBD.