The CNS WHO grading biomarker CDKN2A/B homozygous deletion was detected in 11 IDH-mutant astrocytic gliomas (two primary tumors and 9 recurrences) and one recurrent oligodendroglioma, and hence the tumors were designated as CNS WHO grade 4 and 3, respectively as indicated [1, 40]. Here, IDH1 is linked to oligodendroglioma.