We observed reduced leukemic infiltration (Fig. 6c) and significantly increased levels of fibronectin (P = 0.001, Figs. 6c and S9A), collagen (P = 0.05, Figs. 6c and S9B), and laminin (P = 0.002, Figs. 6c and S9C) in the BMM of mice with B-ALL after treatment with an MMP-9 inhibitor compared with vehicle. Here, MMP9 is linked to precursor B-cell acute lymphoblastic leukemia.