RB1 and liposarcoma: Alternatively, utilizing human liposarcoma cell lines and PDTX mouse models, Zhang et al. demonstrated that continuous chronic exposure to single agent ribociclib (CDK4/6 inhibitor) led to reversion of RB hyperphosphorylation at the CDK4/6-specific sites S780 and S807/811 [42], suggesting that scheduled intermittent dosing may be more beneficial in maintaining cell cycle arrest.