TGFB1 and glioblastoma: An example for the former type is TGF-β2 in GBM, and of the latter the well-known double-negative feedback loops of TGF-β with Snail/miR-34 or Zeb/miR-200, which operate in the induction and maintenance, respectively, of various EMT states along the spectrum from completely epithelial to completely mesenchymal [5].