PDGFRB and glioblastoma: Some GBM subgroups have high levels of PDGF-B/phosphor-PDGF-Rβ [16,17]: Brennan et al. reported that GBMs can be divided into three subgroups by proteomic analysis of GBM samples, and one of these groups was characterized by high levels of PDGF-B and phosphorylation of PDGF-Rβ [16].