Although overexpression of p27Kip1 can induce protection from apoptosis, other studies have reported pro-apoptotic effects where caspases are able to cleave p27Kip1 in a cell type specific manner [9], [61] reported that the inhibition of cytochrome c release might be a possible mechanism of preventing apoptosis with higher p27Kip1 expression in leukemia cells; this indicates that the regulation of the apoptotic process by p27Kip1 might vary with cell transformation status. This evidence concerns the gene CYCS and leukemia.