NOS2 and neoplasm: Ornithine, VEGF, EGF, and TGF-β are examples of tumor-promoting factors derived from macrophages, while nitric oxide generated by inducible nitric oxide synthase in macrophages can inhibit tumor growth.32,33,65,66 Macrophages have been demonstrated to be involved directly or indirectly in several key features of malignant tumors, including angiogenesis, invasiveness, metastasis, regulation of the tumor microenvironment, and therapeutic resistance (Fig. 3).