In recent years, molecular insights into the genome of HR+/HER2− breast cancer have helped to identify promising targets, such as alterations in signaling pathways [phosphatidylinositide 3‐kinase (PI3K/AKT/mammalian target of rapamycin (mTOR)], dysregulation of the cell cycle (CDK4/6), and identification of new ESR1 mutations. This evidence concerns the gene CDK4 and breast cancer.