We observed that, before any tumor lesions could be observed histopathologically, Rb mutant mice displayed elevated Ki67 staining on liver sections compared to Rb wild-type mice; activation of the MYC transgene did not induce proliferation in populations of adult hepatocytes, as expected, and slightly increased the number of Ki67+ cells in Rb deficient mice, but this trend was not significant (Figure 5B). Here, RB1 is linked to neoplasm.