For example, N1 neutrophils produce higher levels of TNFα, NO, and ROS, and are able to kill cancer cells whereas N2 neutrophils express high levels of C-X-C chemokine receptor type 4 (CXCR4 or CD184), gelatinase B/MMP9, among other markers, and act as mediators of tumor progression (Fridlender et al., 2009). This evidence concerns the gene MMP9 and cancer.