We treated two cohorts of Ink4a-ARF deficient BSG-bearing mice with PD-0332991 or vehicle (n= 6 and n=7, respectively) for 48 hours (2 daily doses) and then measured the proliferation of BSG tumor cells 24 hours after the second dose by quantifying the percent of phosphoH3 (pH3)-positive cells in the tumors, a marker for M phase (Figure 3B). Here, CDKN2A is linked to neoplasm.