It has recently been shown that cell signaling in many breast cancers is associated with an activated PI3K/AKT pathway.32 Notably, by evaluating differences in the p-AKT levels between mammary tumors harboring zero, one or two copies of myr-p110α allele combined with either p53fl/fl or p53fl/fl;KrasG12D mutants, our results proved that the levels of PI3K signaling activation are significantly increased and strongly correlated with the increased rate of tumor initiation in a myr-p110α copy number-dependent manner. The gene discussed is PIK3CA; the disease is breast cancer.