Hepatic Myoepithelial Carcinoma in a Dog: Immunohistochemical Comparison With Other Canine Hepatic Carcinomas.

An 11-year-old female miniature Dachshund dog presented with a solid, soft, gray mass on the hepatic lateral left lobe. Histologically, the mass consisted of neoplastic proliferation of cells with round nuclei and eosinophilic and vacuolated cytoplasm arranged in alveolar, trabecular, and solid patterns. Immunohistochemically, the neoplastic cells were positive for pancytokeratin (CK AE1/AE3), CK5, CK14, vimentin, Sox9, and myoepithelial markers (α-smooth muscle actin, p63, and calponin). The morphological and immunohistochemical findings indicated a diagnosis of myoepithelial carcinoma. We conducted immunohistochemical studies on other representative canine hepatic tumors. Although the myoepithelial phenotype was not observed in the hepatocellular carcinoma, some tumor cells in cholangiocarcinoma showed immunohistochemical features of myoepithelium, suggesting that some neoplastic cells in cholangiocarcinoma may have the potential to differentiate into myoepithelial cells. To our knowledge, this is the first report in veterinary medicine of a hepatic carcinoma with a myoepithelial phenotype.