Carcinoid tumor of the common bile duct: evidence for its origin in metaplastic endocrine cells.

Carcinoid tumors of the extrahepatic bile ducts are extremely rare neoplasms. The authors report the case of a 36-yr-old male patient with a carcinoid tumor that arose in the common hepatic bile duct. The non-neoplastic mucosa showed areas of gastric and intestinal metaplasia that included scattered argyrophil endocrine cells. Since the normal mucosa of the bile ducts lacks the latter type of cells, this case provides evidence for the first time that carcinoid tumors of this anatomic site probably originate from metaplastic endocrine cells.