PIK3CG and breast cancer: These pathways have therefore been targeted in ER‐positive BC through agents such as the PIK3 inhibitor, BYL719, in combination with ribociclib and letrozole (AI) (ClinicalTrials.gov : NCT 01872260), or the mTOR inhibitor, everolimus plus ribociclib and exemestane (AI) (ClinicalTrials.gov : NCT 01857193).4, 126