These results thus revealed that miR-2909 plays a key role in the regulation of P21CIP, KLF4, AATF, BCL3, MYC and CCND1, which control the cell cycle and apoptosis in B-ALL, while miR-2909 loses the capacity to regulate the expression of these genes in T-ALL because they harbor a mutated miR-2909-binding site in the 3′UTR of KLF4 and a mutated KLF4 protein. This evidence concerns the gene MYC and acute lymphoblastic leukemia.