MMP9 and cancer: Co-culture of endothelial cells with prostate cancer cells also significantly enhanced expression of MMP-9 and subsequent invasiveness of cancer cells through increased IL-6 secretion from endothelial cells [92], suggesting that growth factors or cytokines secreted by tumor cells, stromal cells, and infiltrating inflammatory cells in the tumor microenvironment collectively regulate MMP-9 gene expression in an autocrine and paracrine manner.