As driver mutations in PIK3Cα, which encodes the catalytic p110 subunit of class I PI3Kα, promote the growth of many cancers including breast cancer because of elevated PI3K activity, we tested whether breast cancer MCF7 cells bearing an oncogenic mutation in PIK3CA (E545K) would be resistant to the ability of an alkaline pHi to increase mTORC1 and/or mTORC2 signaling. This evidence concerns the gene PIK3CA and breast cancer.