ARG1 and neoplasm: Under the influence of various cytokines/growth factors secreted by either tumor cells or macrophages during the course of tumorigenesis, the infiltrating iNOs+ regulatory M1 macrophages get strongly polarized to Arginase-1 & CD206+ M2 macrophages, which are immunosuppressive and promote tumor growth10, 11, 12, 13 in multiple ways.