Bile duct adenomas with endocrine component: Immunohistochemical study and comparison with conventional bile duct adenomas

Bile duct adenomas are small nodules that are usually found incidentally on the liver surface at abdominal surgery or autopsy. We recently analyzed two such lesions that, in addition to the typical small caliber ducts, contained periductular nests and clusters of uniform round cells, suggestive of endocrine cell proliferation. Follow-up of these patients did not show endocrine tumors elsewhere. The lesions were studied by immunohistochemistry (avidin-biotin-peroxidase technique) and compared with conventional bile duct adenomas (seven cases). The results showed these cells to decorate with several endocrine markers, namely, neuron-specific enolase, chromogranin, synaptophysin, and Leu-7. Endocrine markers were not seen in the cells of conventional bile duct adenomas. Epithelial markers, that is, cytokeratin (CAM 5.2 antibody) and epithelial membrane antigen, were expressed by the cells composing both conventional bile duct adenomas and those with endocrine-like cells, although with less intensity in the endocrine cell clusters. We suggest that some bile duct adenomas contain endocrine cell proliferations that morphologically may resemble a small carcinoid tumor or the so-called pulmonary tumorlet. Neurosecretory granules have previously been identified in some cholangiocarcinomas and in bile duct proliferation associated with cholestasis. The endocrine clusters in biliary adenomas may constitute a diagnostic pitfall and must be separated from metastases of carcinoids or islet cell tumors.