Although homozygous deletion of CDKN2A was adopted by the WHO 2021 classification as a defining molecular feature of grade 4 IDH-mutant astrocytomas, this alteration has also been extensively described in IDH-wildtype gliomas, where it is associated with a more aggressive tumor biology and shorter survival, and may therefore serve as an independent poor prognostic biomarker (40). The gene discussed is IDH1; the disease is glioma.