Indeed, in this report we show that tumor necrosis factor (Tnf)α, secreted by B-ALL cells, leads to increased expression of MMP-9 in MSC via activation of the Tnfα receptor (TNFR)1-nuclear factor kappa-light-chain-enhancer of activated B cells nuclear factor kappa B (NF-κB) pathway and increased invasiveness of B-ALL cells. This evidence concerns the gene MMP9 and acute lymphoblastic leukemia.