In most cancers, the RB pathway is defective due to oncogenic changes such as deletion or mutation of pRB, over-expression of cyclin D, mutation of CDK4 making it insensitive to CKIs, and deletion of CKIs [1,56,70,72]. Therefore, activated E2F induces the expression of growth-associated genes, promoting cell proliferation and contributing to tumorigenesis. The gene discussed is RB1; the disease is cancer.