The enhanced cytotoxic effect of Ara-C in FLT3-ITD+ Ba/F3 cells induced by p21 silencing suggests that the up-regulation of p21 expression by FLT3-ITD may confer resistance to Ara-C by inducing quiescence in FLT3-ITD+ AML cells in the patients. This evidence concerns the gene CDKN1A and acute myeloid leukemia.