CDK4 and breast cancer: Breast cancer (BC) is the most frequently diagnosed cancer and poses a significant public health burden.1 Recently, the life expectancy of patients with BC has improved significantly, primarily due to the availability of more effective treatments such as endocrine therapies plus CDK4/6 inhibitors for hormone receptor-positive tumors, antiHER2 drugs for HER2-positive tumors, immunotherapy for triple-negative disease, and PARP inhibitors for BRCA mutated tumors.