Given the published data on tumor cell-specific secretion of MMP-9, we hypothesized that leukemia cells in B-ALL, the most common cancer in children, may remodel the BMM via the production of cytokines or other factors leading to increased expression of MMP-9 by cells of the BMM and, thereby, increased invasiveness of leukemia cells. Here, MMP9 is linked to precursor B-cell acute lymphoblastic leukemia.