CDK4 and breast cancer: Palbociclib was the first FDA approved CDK4/6 inhibitor and highly efficacious in the treatment of HR+/HER2− breast cancers, followed by the structurally related molecules ribociclib and abemaciclib (Dickler et al., 2017; Morrison et al., 2024; Turner et al., 2018; Im et al., 2019; Goel et al., 2022).