The WHO 2021 CNS tumor classification now requires molecular diagnosis. An adult with a diffuse glioma with IDH1 mutation, ATRX loss, and 1p/19q intact is classified as:
- A Astrocytoma, IDH-mutant (graded 2, 3, or 4 based on histological features and CDKN2A/B homozygous deletion) ✓
- B Oligodendroglioma, IDH-mutant and 1p/19q co-deleted
- C Glioblastoma, IDH-wildtype
- D Diffuse midline glioma, H3 K27-altered
Correct answer: A. Astrocytoma, IDH-mutant (graded 2, 3, or 4 based on histological features and CDKN2A/B homozygous deletion)
Explanation
WHO 2021 CNS classification mandates integrated diagnosis. IDH-mutant diffuse gliomas with intact 1p/19q are astrocytomas; ATRX loss and TP53 mutations are characteristic of astrocytomas (not oligodendrogliomas which require 1p/19q co-deletion). Astrocytoma IDH-mutant grade 4 is defined by CDKN2A/B homozygous deletion (regardless of histological features) and is distinguished from IDH-wildtype glioblastoma. Oligodendroglioma requires IDH mutation AND 1p/19q co-deletion. H3 K27 alteration defines diffuse midline glioma.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
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Written and medically reviewed by the StethoPrep medical team.