FAS and mesenchymal cell neoplasm: Based on their respective genomic and RNA signatures, four distinct subtypes (classical, mesenchymal, neural and proneural) have been proposed for GBM.27 When classified according to these subtypes, CD95 was predominantly expressed in mesenchymal tumors in the TCGA GBM data set while CD95 expression was the lowest in proneural GBM (Figure 1b).