We confirmed increased levels of fibronectin (P = 0.002, Figs. 2e and S4E), laminin (P = 0.043, Figs. 2e and S4F) and collagen (P = 0.061, Figs. 2e and S4G) in MMP-9-deficient compared with wild type mice with B-ALL (Fig. 2e). Here, MMP9 is linked to precursor B-cell acute lymphoblastic leukemia.