MPO and neoplasm: There is typical crosstalk between cancer progression, ROS accumulation, and chronic inflammation Under tumor microenvironment, inflammatory cells direct a massive generation of ROS by the activation of oxidant-generating enzymes such as upregulation of lipoxygenase (LOX), myeloperoxidase (MPO), cyclooxygenase 2 (COX2), xanthine oxidase (XO), NADPH oxidase, and inducible nitric oxide synthase (iNOS) to disrupt the physical, chemical, and biological factors.