MMP9 and breast cancer: For instance, the overexpression of matrix metallopeptidase 11 (MMP-11) in macrophages increases migration of human epidermal growth factor receptor 2 (HER2)-positive breast cancer cells by activating the MAPK pathway via binding of the chemokine CCL2 to its receptor on cancer cells, followed by activation of the MAPK pathway and upregulation of MMP-9 [38].