IDH1 and astrocytoma (excluding glioblastoma): Homozygous deletion of CDKN2A/B, which has recently been established as a biomarker of grading and prognosis in 2021 WHO IDH-mutant astrocytic gliomas20, was heterogeneous in one out of two IDH-mutant astrocytomas, CNS WHO grade 4 (GU-LGG-90), as two of the three biopsies presented homozygous deletion of CDKN2A/B (Fig. 5A).