In addition, the majority of chronic HBV-infected tree shrews in this study showed a relatively high level of cell proliferation markers such as Ki67, Cyclin D1 and P53, and HBx protein (a protein that has been associated with HCC in humans and the woodchuck) in liver tissues in comparison to the tree shrews without HBV infection (data not shown). This evidence concerns the gene CCND1 and hepatocellular carcinoma.