Mixed adenoneuroendocrine carcinoma of the distal bile duct: a case report

BACKGROUND: Mixed adenoneuroendocrine carcinoma (MANEC) of the common bile duct (CBD) is very rare, with only 10 reported cases. Here, we report a case of MANEC of the distal bile duct (DBD) that was surgically resected under a diagnosis of cholangiocarcinoma (CCA). CASE PRESENTATION: A 60-year-old male had epigastric pain and was admitted to our hospital for the treatment of a suspected CBD stone. Upon admission, laboratory findings revealed elevated hepatobiliary enzymes including serum aspartate aminotransferase, serum alanine aminotransferase, serum glutamyltransferase, and serum alkaline phosphatase. Both carcinoembryonic antigen and carbohydrate antigen 19-9 were negative. Computed tomography (CT) showed dilation of the CBD. Endoscopic retrograde cholangiopancreatography (ERCP) showed circumferential stenosis and a 5-mm elevated lesion in the DBD. Brush cytology showed atypical ductal cells, indicating adenocarcinoma (AC) of the DBD. Under a diagnosis of CCA of the DBD, a subtotal stomach-preserving pancreaticoduodenectomy was performed. Neither peritoneal dissemination nor lymph node metastasis was found. Microscopically, the lesion was seen to be composed of predominantly well-differentiated tubular AC in the superficial layer of the tumor, admixed with neuroendocrine carcinoma (NEC) in the deeper portion, indicating a diagnosis of MANEC of the DBD. After immunohistochemical staining, NEC components were positive for synaptophysin and CD56 and were for SSTR2, SSTR5, and mammalian target of rapamycin (mTOR). Three months postsurgery, postoperative adjuvant chemotherapy with S-1 was started. More than 3 years postsurgery, he is alive without recurrence. CONCLUSIONS: MANEC is highly malignant, progresses rapidly, and has a poor prognosis. Preoperative diagnosis is difficult; therefore, identifying NEC components by immunohistochemical staining using resected specimens is important.