MMP9 and breast cancer: On the other hand, in breast cancer, Barx2 increases the expression of both estrogen receptor–α gene (ESR1) isoforms, and modulates the expression of the estrogen-responsive genes SOX5, RBM15, Dynein, mortalin, and active matrix metalloproteinase-9 (MMP9) and the tissue inhibitor of metalloproteinase (TIMP) genes.