RB1 and cancer: In the MCF10A cell line (an immortalised non-cancer human mammary epithelial cell line), most cells (∼75% of physiologically-cycling cells), which experience a cell cycle with sufficient mitogen provision and limited replication stress-induced DNA damage, successfully maintain Rb hyperphosphorylation in mitosis and pass CP1, proceeding to G1 phase in daughter cells (19,22,23,36,40,42,48).