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Many advances have been made in the characterisation of primary liver tumours in humans, in particular relating to the identification and role of hepatic progenitor cells, resulting in a new classification. The aim of the present study was to investigate the presence and relative frequency of morphological types of canine primary hepatic neoplasms and to determine whether a classification similar to the human scheme can be applied to these canine neoplasms. Canine primary liver tumours (n=106) were examined histologically and with the immunohistochemical markers keratin 19, HepPar-1, epithelial membrane antigen/mucin-1, CD10, neuron-specific enolase and chromogranin-A. Eleven nodular hyperplasias and 82 tumours of hepatocellular origin were diagnosed. The latter were subdivided in hepatocellular tumours with 0-5% positivity for K19 (n=62), which were well differentiated and had no evidence of metastasis, tumours with >5% positivity for K19 (n=17), which were poorly differentiated and had intrahepatic and/or distant metastasis, and a scirrhous subgroup (n=3) with an intermediate position with regard to K19 staining and malignancy. Ten cholangiocellular tumours (nine cholangiocellular carcinomas and one cholangiolocarcinoma) were diagnosed and all had intrahepatic and/or distant metastases. Three neuroendocrine carcinomas were also diagnosed. Histopathological and immunohistochemical examination of canine primary hepatic neoplasms can differentiate hepatocellular, cholangiocellular and neuroendocrine tumours, in accordance with the most recent human classification system.