Small-cell carcinoma of the extrahepatic bile duct: a case report and review of the literature

A small-cell carcinoma of the extrahepatic bile duct in a 69-year-old woman is herein reported. A tumor measuring approximately 3 cm in diameter was located at the confluence of the common bile duct, cystic duct, and common hepatic duct. Histopathologically, the tumor was small-cell neuroendocrine carcinoma without any gland formation or differentiation to squamous cell carcinoma. Tumor cells were immunoreactive for epithelial markers such as epithelial membrane antigen and cytokeratin and for the neuroendocrine markers such as neuron-specific enolase, chromogranin A, and synaptophysin. Although the carcinomas in more than half of the reported cases have been reported to be associated with well-to-moderately differentiated squamous or glandular components, seven cases, including our case, showed the carcinomas without squamous or glandular components. According to the review of 16 previously reported cases and our case of small-cell carcinoma of the extrahepatic bile ducts, there is no significant difference in the clinicopathological findings, namely, age, sex, site of carcinoma, and prognosis between the cases with or without squamous or glandular components. No CD34-positive multipotent adult progenitor cells, which might be the origin of the small-cell carcinoma, were detected in the bile duct epithelium in our case.