In breast cancer cell lines, MCF-7 and MDA-MB-436, 5-aza-2′-deoxycytidine induced the demethylation of CpG sites in the MMP9 promoter and histone H3 lysine-4-trimethylation (an epigenetic marker of open chromatin-allowing gene transcription) [12], resulting in increased MMP9 expression [37]. This evidence concerns the gene MMP9 and breast cancer.