IDH1 and anaplastic oligodendroglioma: This agrees with previous studies, which show a clear association between IDH1 mutation and favorable clinical outcome (van den Bent et al., 2010; Qi et al., 2011; SongTao et al., 2012; Yan et al., 2012; Wang et al., 2014; Yang et al., 2015). IDH1 mutation has been shown to be associated with better OS in grade III anaplastic oligodendroglioma and anaplastic oligoastrocytoma (van den Bent et al., 2010; Wang et al., 2014), grade IV glioblastoma (SongTao et al., 2012; Yan et al., 2012), grade I glioma (Qi et al., 2011), and grade II glioma (Wang et al., 2014).