Abstract
A composite glandular-endocrine cell carcinoma of the extrahepatic bile duct in a 64 yr old Japanese man is reported. A nodular polyp measuring 1.9×1.1 cm was located in the confluence of the extra-hepatic bile duct. Histologically, the tumor was composed of well differentiated tubular adenocarcinoma and small cell neuroendocrine carcinoma with a transition between the 2 components. The 2 areas of the tumor immunohistochemically revealed a clear-cut difference in functional differentiation. Tumor cells in the glandular component were immunoreactive to both carcinoembryonic antigen (CEA) and CAM 5.2, while those in the small cell area were immunoreactive to neuroendocrine markers such as neuron specific enolase (NSE), chromogranin A and serotonin. These results suggest that the tumor arose from a multipotential stem cell capable of differentiation in 2 directions.