Rb protein is a tumor suppressor that plays a crucial role in the G1/S transition as it was found to be responsible for the progression through G1 phase and then also through G1 restriction point [58] since the phosphorylation of Rb protein led to the increase in transcriptional activity of E2F that promotes the expression of, e.g., cyclin E [59]. Here, RB1 is linked to neoplasm.