CASP8 and glioblastoma: In general, GBM cells have been found to be highly resistant to TRAIL-induced apoptosis due to a variety of reasons, such as moderate to low expression of DR4 and DR5 (Knight et al. 2001; Kuijlen et al. 2006), the up-regulation of the anti-apoptotic proteins c-Flip, Bcl-2 and survivin (Knight et al. 2001; Kouri et al. 2012; Song et al. 2003; Xie et al. 2006; Fulda et al. 2002), or the down-regulation of critical pro-apoptotic proteins such as caspase-8 and Bak (Knight et al. 2001; Song et al. 2003; Capper et al. 2009; Qi et al. 2011).