IDH1 and gliosarcoma: In accordance with a central role of the TWEAK/Fn14 system for the motility and aggressiveness of glioblastoma cells, Fn14 expression is strongly increased in gliosarcoma, a particularly aggressive form of high grade glioma, isocitrate dehydrogenase 1 (IDH1) wild-type glioblastoma, which have a poorer prognosis than IDH1 mutated glioblastoma, mesenchymal type glioblastomas and recurrent glioblastoma (Tran et al., 2006; Fortin et al., 2009; Perez et al., 2016; Hersh et al., 2018a).