IDH1 and central nervous system cancer: Although all G-CIMP-low tumors were classified as grade IV (10 of 20 IDH mutant GBMs at first recurrence, 50%), not all IDH mutant grade IV first recurrent gliomas progressed to the G-CIMP-low phenotype; in fact, 35% (7 of 20) of grade IV IDH mutant gliomas at first recurrence were classified as G-CIMP-high, whereas 15% (3 of 20) were classified as G-CIMP-intermediate tumors (Figure 2A).