Since PAK6 inhibition can induce a corresponding decrease in MDM2 protein expression and a significant increase in p21 protein expression in the presence of p53 in CD34+ CML patient cells, a similar observation was made in our cell line model system without expression of p53, suggesting that the activity of the MDM2-p21 axis is mainly independent of p53. This evidence concerns the gene TP53 and chronic myelogenous leukemia, BCR-ABL1 positive.