WHO classification 2021 has not yet designated definite molecular criteria for anaplastic oligodendroglioma.1 Deletions in CDKN2A/B, increased MYC signaling, and mutations in FUBP1, NOTCH1, PIK3CA, and TCF12 have all been associated with tumor progression or poorer survival in oligodendroglioma.1 CDKN2A/B HD is now established by WHO as a molecular criterion for IDH-mutant Grade 4 astrocytomas. The gene discussed is TCF12; the disease is oligodendroglioma.