CDK4 and breast cancer: Pivotal studies evaluating cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) palbociclib, ribociclib, and abemaciclib, which are approved by the US Food and Drug Administration (FDA) in combination with the selective estrogen-receptor degrader fulvestrant or aromatase inhibitors (AIs) for treatment of HR+/HER2− metastatic or advanced breast cancer (MBC; ABC), did not provide data on male patients [7–9].