MMP9 and neoplasm: It has been found that N2 neutrophils promote tumor angiogenesis, modify the extracellular matrix of the tumor microenvironment (TME) to promote tumor cell proliferation and control the early-stage biological characteristics of tumor cells, and promote tumor cell invasion and metastasis in the late-stage through the secretion of various inflammatory mediators (e.g., PGE2, CCL17, VEGF, Arg-1, iNOS, and B/MMP9 gelatinase) [36].