CDK4 and breast cancer: Currently, cyclin-dependent kinase 4 and 6 inhibitor (CDK4/6i)-based endocrine therapy (ET) represents the standard of care in the first-line setting for patients with hormone receptor-positive/human epidermal growth factor receptor 2-negative (HR+/HER2−) advanced breast cancer, demonstrating significant improvements in both progression-free survival (PFS) and overall survival (OS) [11].