Several studies suggest a functional role of miR-21 in myeloid leukemias: miR-21 is over-expressed in the blastic phase of CML [25]; it is also frequently overexpressed in AML blasts [26]; miR-21 knock down sensitizes CML CD34+ to imatinib [27], K562 cells to arsenic-induced cell death [28], and induces apoptosis of K562 cells [29]. This evidence concerns the gene CD34 and myeloid leukemia.