Although data suggest that complete suppression of p-Rb upon dinaciclib treatment correlates closely with induction of apoptosis in solid tumor cell lines and xenograft models [27–29], we could not consistently demonstrate such a relationship between p-Rb inhibition and cell death in patients’ PBMC in vivo or in primary leukemia cells or cell lines treated in vitro, including at the times when Mcl-1 down-regulation was clearly present. This evidence concerns the gene RB1 and leukemia.