To address these issues, a panel of ER-positive breast cancer cell lines with different PI3K pathway mutations were tested against three different PI3K pathway inhibitors, with selectivity against either the rapamycin-sensitive mammalian target of rapamycin (mTOR) complex (Everolimus/RAD001), the PI3K catalytic isoforms (BKM120) or both PI3K and mTOR (BGT226) in the presence or absence of estrogen or ER downregulation by fulvestrant. This evidence concerns the gene MTOR and breast cancer.