PIK3CA and breast cancer: Activation of the PI3K pathway is reported to be a hallmark of HR + BC cells that are resistant to endocrine therapy.70 PI3K pathway is frequently activated aberrantly in BC, with majority of mutations in the PI3K catalytic subunit (PIK3CA), encoding the catalytic p110α subunit.71 Approximately, 20%‐25% breast tumors exhibit these mutations depending on the BC subtype.71 Blocking ER and PIK3CA pathways therefore seems a promising strategy.