The role of MMP-2 (together with MMP-9 and TIMP-1) in the clinical progression of pediatric ALL was examined by Saleh et al. Bone marrow samples were obtained from 76 patients, and those with MMP-2 overexpression showed a significant increase in the BM blast cell count at D0 and at D15 of treatment, as well as a significant increase in MRD at D15, compared to those with MMP-2 low-expression. The gene discussed is MMP9; the disease is acute lymphoblastic leukemia.