Data from one phase II and three phase III clinical trials have demonstrated that adding a CDK4/6 inhibitor (palbociclib or ribociclib) to letrozole results in significant improvements in PFS vs an AI.41, 99, 100 Furthermore, recent evidence from the MONALEESA‐3 trial has also supported and emphasized on combining CDK4/6 inhibitor (ribociclib) with fulvestrant as a first‐line treatment option for HR+/HER2− advanced BC. This evidence concerns the gene CDK4 and breast cancer.