CDK4 and breast cancer: With the new molecular hallmarks being extensively explored, significant progress for BC drug therapy has been made in recent years, including targeted therapies such as CDK4/6 (cyclindependent kinase 4/6) inhibitors, anti-programmed cell death ligand 1 (PD-L1) immunotherapy, phosphatidylinositol 3-kinase inhibitors (PI3K), chemotherapy, and endocrine therapy (Loibl et al., 2021).