Matrix metalloproteinase-9 (MMP-9) produced by leukemia cells facilitates tumor progression via remodeling of the ECM of the BM microenvironment, and MMP-9 deficiency in the BM microenvironment reduces leukemia-initiating cells and prolongs survival of mice with BCR-ABL1-positive B-cell acute lymphoblastic leukemia (B-ALL)75. The gene discussed is MMP9; the disease is precursor B-cell acute lymphoblastic leukemia.