PPM1D and neoplasm: In view of findings above that p53 activity is higher in Wip1−/− MEFs compared to Wip1+/+ MEFs; one interpretation of these in vivo tumor results is that homozygous loss of Wip1 (i.e.Tax+Wip1−/−) reduces the level of p53-inactivation in Tax expressing cells compared to counterpart cells that expresses both Wip1 and Tax (i.e. Tax+Wip1+/+); this reduced inactivation of p53 could explain the increased tumor-free survival observed in the Tax+Wip1−/− over the Tax+Wip1+/+ mice.