In postmenopausal women receiving AI as initial therapy for ER+ mBC, adding a CDK4/6 inhibitor improved PFS in 3 randomized phase III trials (PALOMA [PALbociclib: Ongoing trials in the MAnagement of breast cancer]-2, MONARCH 3, MONALEESA-2) (22-24). This evidence concerns the gene ESR1 and breast carcinoma.