Combined hepatocellular-cholangiocarcinoma in a cow.

We examined a 10-year-old cow in which about half of the liver was displaced by malignant tissue consisting of hepatocellular carcinoma (HCC) and cholangiocarcinoma (CC). Cytokeratin (CK) 18 and 7 were expressed in the latter. Metastasis was present in the hepatic, pancreaticoduodenal and mediastinal lymph nodes, where malignant cells had hepatocellular features, but more pleomorphic and atypical than in the primary lesion. Areas composed solely of CC cells or less-differentiated HCC cells were observed. In contrast, well-differentiated HCC cells were almost always admixed with the other two types, and may have had the ability to transform into CC cells and to dedifferentiate into less-differentiated cells. This report suggests that CK18 is an excellent marker for biliary differentiation in cattle.