RB1 and cancer: Cancer cells are frequently characterized by i) the presence of activating mutations of gene coding for the components of the proliferating and growth factor signaling pathways, ii) the disruption of pRb function consequent to RB1 mutation or deletion, overexpression of cyclin D1, cdk4, and cyclin E, and INK4a mutation, gene deletion, or silencing [65, 66], and iii) inactivating mutations of p53 [67, 68].