Recent studies have shown that macrophages can be recruited and induced to become the M2 type by a wide variety of factors secreted by glioma cells, including IL-10, IL-4, IL-6, macrophage-colony stimulating factor (M-CSF), TGF-β, and prostaglandin E2 (PGE2), and promote cancer cell proliferation in GBMs (35, 36). This evidence concerns the gene TGFB1 and glioma.