In MCF-7 breast cancer cells, oleuropein inhibits the migration ability of cells by suppressing EMT through increasing the expression of p53, which increases miR43a expression that leads to the downregulation of sirtuin-1 (SIRT1), resulting in the downregulation of mesenchymal markers (for example, matrix metalloproteinase-2 and -9 (MMP-2 and MMP-9)), downregulation of the EMT inducer (ZEB1), and upregulation of the epithelial marker (E-CAD) [92,135]. This evidence concerns the gene MMP9 and breast cancer.