Our present results clearly show that MMP-9, both in MEC-1 transfectants and in primary CLL cells, not only prevented downregulation of anti-apoptotic proteins (Mcl-1, Bcl-xL, Bcl-2) in response to ATO but also upregulated their levels with respect to basal expression. This evidence concerns the gene MCL1 and B-cell chronic lymphocytic leukemia.