TP53 and breast cancer: In accordance with this result, addition of two copies of myr-p110α into homozygous p53 deletion (p53fl/fl;myr-p110αfl/fl) also facilitated mammary tumor initiation compared with p53fl/fl;myr-p110αwt/fl (135.1±6.2 days vs 259.6±10.6 days; Figure 3b).