These reagents, including cell-cycle inhibitors (e.g., CDK4/6 inhibitors: Palbociclib, Abemaciclib and Ribociclib), telomerase inhibitors, cytokines, epigenetic modulators, DNA-damaging chemicals and specific factors that activate the p53/p21-Rb or p16INK4a-Rb pathway, have been evaluated in the pre-clinical studies and clinical trials for their therapeutic value in cancer (Table 1) [101]. The gene discussed is CDK4; the disease is cancer.