In addition to defending against microbial invasion through phagocytosis and degranulation, neutrophils can undergo apoptosis after activation, and then form neutrophil extracellular traps (NETs), fibrinoid structures comprising extracellular chromatin and granulocyte proteins, including myeloperoxidase and neutrophil elastase, which were discovered because of their pathogen-trapping function, which can promote tumor metastasis by capturing circulating tumor cells and causing their proliferation at a second site (83, 90). Here, MPO is linked to neoplasm.