A 45-year-old patient's brain tumor shows IDH1 mutation, 1p/19q co-deletion, TERT promoter mutation, and no ATRX loss. According to WHO 2021 CNS tumor classification, this tumor is classified as:
- A IDH-mutant astrocytoma, CNS WHO grade 2
- B Glioblastoma, IDH-wildtype
- C Oligodendroglioma, IDH-mutant and 1p/19q codeleted, CNS WHO grade 2 or 3 ✓
- D Diffuse midline glioma, H3 K27-altered
Correct answer: C. Oligodendroglioma, IDH-mutant and 1p/19q codeleted, CNS WHO grade 2 or 3
Explanation
Per WHO 2021 CNS Tumor Classification, oligodendroglioma is defined by the molecular triad: IDH mutation + 1p/19q codeletion (due to unbalanced translocation of chromosomes 1 and 19). TERT promoter mutation is an additional characteristic but not required. Critically, ATRX loss distinguishes IDH-mutant astrocytomas (which have ATRX mutations) from oligodendrogliomas (which retain ATRX). The 2021 WHO classification requires molecular criteria for definitive glioma diagnosis. IDH-mutant astrocytoma has IDH mutation + ATRX loss without 1p/19q codeletion.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
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Written and medically reviewed by the StethoPrep medical team.