PIK3CA and breast cancer: Since P53 loss and activation of the PTEN-PI3K-AKT pathway occur in a significant proportion of breast cancers, in this study we generated MMTV-TVA+/-; mT/mG+/-; Tp53F/F; PtenF/F mice, and used RCAS-Cre virus to knock out both Tp53 and Pten genes in MGECs in these mice when they were sexually matured.