In fact, TGF-β, which is well present in the GBM environment and secreted by microglia, stromal and tumor cells [133], is able to induce the mesenchymal transition, via SMAD2 phosphorylation and recruitment of ZEB1, especially in GBM with a low or absent expression of mesenchymal markers [134]. Here, SMAD2 is linked to glioblastoma.