ARG1 and neoplasm: N1 neutrophils show an anti-tumor phenotype with their capability of efficiently killing microorganisms and tumor cells, while N2 neutrophils show a pro-tumor phenotype 14 with synthesizing numerous cytokines, such as matrix metalloproteinase 2/9 (MMP-2/9), arginase 1 (arg-1), neutrophil elastase (NE), vascular endothelial growth factor (VEGF) and so on 15.