MMP9 and cancer: Thus, the forced overexpression of quiescin 6 in human MCF-7 breast cancer cells rendered them more resistant to apoptosis arising from oxidative stress compared to control transfected cells, thereby implicating QSOX1 in cell survival [11] whilst the suppressed expression of quiescin in pancreatic cancer cell lines BxPC-3 and Panc-1 inhibited cancer cell invasion by activation of MMP-2 and MMP-9 Matrix Metalloproteinases [43].