MMP9 and neoplasm: Morphine regulates the recruitment of tumor by immune cells and endothelial cells, and regulates the invasion and metastasis of tumor tissue by regulating extracellular matrix degrading enzymes, such as MMP-9 and urokinase-plasminogen activator(u-PA) through modulation of paracrine communication between cancer cells and nonmalignant cells in the tumor microenvironment [3].