TGFB1 and glioblastoma: In summary, this study provides important new information on the biology of TGF-β in glioblastoma, in particular that (i) all three isoforms are expressed and biologically active, (ii) their expression seems to be commonly controlled, and (iii) determination of either TGF-β or TGF-β target gene mRNA expression may help to enrich for subgroups of glioblastomas characterized by TGF-β pathway activation.