ARG1 and neoplasm: Traditionally, polarized macrophages have been classified as the classically activated M1 macrophages, which express high levels of MHC class II molecules and other markers such as inducible nitric oxide synthase (Nos2) and possess tumoricidal activity; and the alternatively activated M2 macrophages which have low expression of MHCII, high levels of Arginase 1 (Arg1), and favor tumor progression [15].