MMP9 and bacterial urinary tract infection: Our previous study showed that UTI exerts significant inhibitory effects on 1) the proliferation and invasion of human breast cancer cell lines MCF-7 and MDA-MB-231, 2) the growth of MCF-7 transplanted tumor in nude mice, 3) the gene and protein expression of CXCR4 and MMP-9 in breast cancer cells; UTI also enhances the anti-tumor effect of the chemotherapy drug cyclophosphamide [4,5].