CDK4 and breast cancer: Our study found that ezetimibe can also inhibit the growth of breast cancer cells and block cells in the G1 phase, while inhibiting the expression of CDK2, CDK4 and CyclinD1 proteins, so we speculate that ezetimibe-induced G1 blockade of breast cancer cells may occur by inhibiting CyclinD1 and releasing p27 in CDK4/6-CylinD1 complex, inducing the upregulation of p27 to inhibit CDK2, thereby inhibiting the proliferation of breast cancer cells.