Tang and co-workers [98] reported that, in breast cancer cells, quercetin significantly inhibited the protein expression of MMP-2 and MMP-9 and increased the TIMP-1 and TIMP-2 levels in a concentration-dependent manner; it also suppressed the activity of MMP-2 and MMP-9 based on gelatin zymography. The gene discussed is MMP9; the disease is breast cancer.