In several randomized phase III trials (PALOMA-2, MONALEESA-2, MONALEESA-7 and MONARCH-3), the combination of a nonsteroidal aromatase inhibitor (NSAI) with CDK4/6is (palbociclib, ribociclib, or abemaciclib) as a first-line strategy in the treatment of HR+ and HER2-negative metastatic BC showed a significantly longer PFS [14,15,16,17]. This evidence concerns the gene ERBB2 and breast cancer.