Hepatocellular carcinoma in a Hokkaido brown bear (Ursus arctos yesoensis)

Hepatocellular carcinoma with metastases to lymph nodes and adrenal glands was found in a 26-year-old male Hokkaido brown bear (Ursus arctos yesoensis). Left hepatic lobe was largely replaced by well-differentiated neoplastic cells, whereas poorly differentiated tumor cells had proliferated in part of the left hepatic lobe, in scattered nodules in the remaining liver tissue, and at the metastatic sites. Immunoreactivity for hepatocyte antigen (hepatocyte paraffin 1 antibody) and alpha-fetoprotein was observed in both well- and poorly differentiated neoplastic cells in the liver and metastatic foci. To our knowledge, this case is the first report of hepatocellular carcinoma in brown bears.