MMP9 and neoplasm: The role of tumor-associated neutrophils includes: (1) inducing vascular endothelial growth factor, promoting angiogenesis, increasing tumor invasion, and weakening T lymphocytes resulting in promotion of tumor progression [37]; (2) reactive oxygen species production leading to damage of cellular DNA [5, 36]; and (3) secretion of various proteases, including neutrophil elastase, and matrix metalloproteinase-9.