RB1 and neoplasm: Hyperphosphorylation of the RB protein inhibits mitogenic signaling, disrupting the transcriptional repression of RB complexes that further allows the phase transition from G1 to S. It was also reported that childhood retinal cancer is caused by RB1 mutation and this gene produces a phosphoprotein that inhibits cell cycle progression, essential for the typical RB-mediated tumor-suppressive action.