Ribociclib induces dephosphorylation of phosphorylated Rb (pRb) and concomitant G1 cell-cycle arrest in RB1-proficient JeKo-1 mantle cell lymphoma cells, while no effect on cell-cycle progression was observed in the RB1-deleted lung adenocarcinoma cell line NCI-H2009 up to 10 μM (Brain C et al, manuscript in preparation). The gene discussed is RB1; the disease is mantle cell lymphoma.