In the PALOMA-2, MONALEESA-2, MONARCH-3, and MONALEESA-7 phase III trials, the addition of CDK4/6is (palbociclib, ribociclib, abemaciclib) to ET significantly improved PFS when used as first-line therapy in both pre- and postmenopausal breast cancer patients [56,57,58,59]. Here, CDK4 is linked to breast cancer.