MMP9 and breast cancer: Some of the antimetastatic actions of melatonin involve the inhibition of cancer stem cells proliferation, as well as migration, matrix metalloproteinase 9 (MMP9) activity and expression of genes associated with epithelial-mesenchymal transition (EMT) in ovarian cancer cells12, as well as the upregulation of a suppressor of metastasis (kisspeptin) in MDA-MB-231 breast cancer cells14.