RB1 and breast cancer: Ectopic expression of the phospho-deficient CDH1-7A mutants that can bind to the APC/C core and are constitutively active14, induced a senescence-like state, indicative of an irreversible G0 state in both RB-proficient and RB-deficient BC cell lines (Fig. 2b, c, Supplementary Fig. 4a), which indicates an RB-independent cell cycle exit.