MMP9 and cancer: In addition, Gab2 facilitates the epithelial-mesenchymal transition (EMT) of cancer cells, the key process in cancer metastasis; this is mediated by enhanced MMP expression, mainly MMP-9, via activation of the mitogen-activated protein kinase (MEK) and extracellular signal-regulated kinase-1/2 (ERK1/2) signaling pathways [46].