MMP9 and neoplasm: For example, neutrophils affect tumor development by secreting a variety of factors, such as matrix metalloproteinase-9 (MMP-9), reactive oxygen species (ROS) and reactive nitrogen species (RNS), which promote tumor growth, metastasis, angiogenesis, and immunosuppression (38–40), and monocytes can secrete a variety of growth factors and cytokines, such as IL-6, TNF-α, vascular endothelial growth factor (VEGF) and platelet-derived growth factor (PDGF), which can stimulate tumor cell proliferation and metastasis.