Loss of p53 activity yielded an increased penetrance of breast cancer phenotypes and decreased latency—MYB-NFIB/MMTV-Cre/p53+/fl mice had penetrance of 27.3% and a latency of ~44 weeks, while MYB-NFIB/MMTV-Cre/p53fl/fl mice had penetrance of 45.5% and a latency of 16-39 weeks (Figure 1E). This evidence concerns the gene NFIB and breast carcinoma.