NOS2 and neoplasm: Concretely speaking, M1 macrophages have a pro-inflammatory and anti-tumor effect through the expression of inducible nitric oxide synthase (iNOS), whereas the M2 macrophages (anti-inflammatory and pro-tumor) are beneficial to the growth of tumor cells and express high levels of anti-inflammatory cytokines (such as IL-10) and strong arginidase-1 (arg1) activity (60–62).