MMP9 and cancer: In particular, while the N1 profile is characterized by reduced proliferation and by the secretion of high levels of tumor necrosis factor-alpha (TNF-α), N2 cells are long-living and can favor cancer development by releasing specific pro-tumor factors, such as reactive oxygen species (ROS), neutrophil extracellular traps (NETs), IL-6, IL-8, and matrix metalloproteinase 9 (MMP-9) [8].