MMP9 and cancer: Previous studies have reported that MMP-9 decreased apoptosis in cancer cells [38]; reduced proliferation and metastasis in cancer cells derived from MMP-9 deficient mice compared to those from wild-type mice [39, 40]; promoted angiogenesis in two transgenic models of cancer progression [38, 39]; inhibited T cell activity against tumors by enhancing IL-2Rα and TGF-β production [41]; and could significantly suppress the cytotoxicity of NK cells in oral squamous cell carcinoma cell lines [20].