Though highly expressed in glioma tissue and tumor-associated microglia, Tgf-β is not expressed in the normal brain.93 This expression pattern combined with studies showing that downstream Smad activation leads to PDGF-b-driven proliferative and invasion is suggestive of a role in tumor initiation.94 In addition, Tgf-β can upregulate VEGF, mediating angiogenesis, and can promote generation of Tregs. This evidence concerns the gene TGFB1 and glioma.