MMP9 and neoplasm: The increment of circulating MMP-9 was released by tumor cells or stromal cells, and its activity could be downregulated by many extracellular factors, such as MMP-1, 3, 7, 10, 26, trypsin-2 and neutrophil elastase [37], among them, the tissue inhibitors of metalloproteinases 1 (TIMP1) is the most important endogenous inhibitor against MMP-9.