CDK4 and breast cancer: Many HR+ BC patients experience relapse within a decade of diagnosis [67], and the application of targeted therapies like Cyclin-dependent kinases 4 and 6 (CDK4/6) inhibitors (e.g., ribociclib, abemaciclib, and palbociclib) in combination with endocrine therapy (ET, e.g., like tamoxifen and aromatase inhibitors (AIs)), has changed the management of these patients.