CDK4 and skin basal cell carcinoma: The cell cycle protein D1 (cyclin D1) is overexpressed in most human BCCs, and cyclin D1 stimulates BCC proliferation by activating the cell cycle protein-dependent kinase 4/6 (CDK4/6) [68], whereas CDK4/6 inhibition induces cell cycle arrest in G1 cells, thereby inhibiting BCC proliferation [69].