ARG1 and central nervous system cancer: In an in vitro model of glioma at all stages, pharmacologic blocking of mTOR decreases urea and ARG1 levels (considered a biomarker of the M2 polarization state of microglia), decreases the M2 polarization phenotype of microglia by 40% and increases the proportion of the M1 phenotype realizing its direct antitumor effects (78).