To check whether there would be a correlation between the extent of PI3K signaling activation and the rate of tumor initiation, we evaluated the PI3K signaling activation status by comparing the levels of p-AKT between p53fl/fl;myr-p110αwt/fl, p53fl/fl;myr-p110αfl/fl, p53fl/fl;KrasG12D;myr-p110αwt/fl and p53fl/fl;KrasG12D;myr-p110αfl/fl mammary tumors. This evidence concerns the gene PIK3CA and breast cancer.