Arginine is a critical substrate that functions during macrophages' M1 and M2 polarization; M1 macrophages activate iNOS, a cancer-supporting factor [6, 7], to catalyze arginine, producing NO to attack cancer cells, whereas M2 macrophages express arginase 1, converting arginine to ornithine to further promote the cancer cells [5]. The gene discussed is ARG1; the disease is cancer.