NEWFlashcards for any set of questions, quick-reference tables for breast, lung and prostate, and a month of access for every colleague you refer. See what changed

CNS: WHO 2021 molecular classification

Free question published 09 October 2026

Central nervous systemWHO 2021 molecular classification

A 41-year-old man has a frontal lobe tumour resected. Histology shows a diffuse astrocytic glioma with brisk mitotic activity but no microvascular proliferation and no necrosis. Immunohistochemistry confirms an IDH1 R132H mutation and ATRX loss; 1p/19q is intact and CDKN2A/B is not homozygously deleted. Under the WHO 2021 classification of CNS tumours, which integrated diagnosis is most appropriate?

  1. ADiffuse astrocytoma, IDH-wildtype, WHO grade 2
  2. BAnaplastic oligoastrocytoma, NOS
  3. CAstrocytoma, IDH-mutant, WHO grade 3
  4. DOligodendroglioma, IDH-mutant and 1p/19q-codeleted, WHO grade 3
  5. EGlioblastoma, IDH-wildtype, WHO grade 4

Why C is correct

Under WHO 2021 (CNS5) and the EANO glioma guideline, an adult diffuse glioma with an IDH1 codon 132 mutation that is NOT 1p/19q-codeleted is classified as astrocytoma, IDH-mutant. Grading is then within tumour type: brisk mitotic activity with no microvascular proliferation, no necrosis and no CDKN2A/B homozygous deletion places this at WHO grade 3, since any of microvascular proliferation, necrosis or CDKN2A/B homozygous deletion would define grade 4. The presence of an IDH mutation excludes glioblastoma, IDH-wildtype, and the intact 1p/19q excludes oligodendroglioma.

And why the others are not

  • AIncorrect: the tumour is IDH-mutant, not IDH-wildtype, and the brisk mitotic activity is incompatible with grade 2.
  • BIncorrect: the combined oligoastrocytoma category has been abandoned in WHO 2021 in favour of molecularly defined entities.
  • DIncorrect: oligodendroglioma requires both IDH mutation and 1p/19q codeletion, and 1p/19q is intact.
  • EIncorrect: glioblastoma is reserved for IDH-wildtype astrocytic gliomas; the IDH1 R132H mutation here excludes that diagnosis.

Source WHO Classification of Tumours of the Central Nervous System, 5th edition (CNS5) — adult diffuse glioma criteria — Louis DN, Perry A, Wesseling P, et al. The 2021 WHO Classification of Tumors of the Central Nervous System: a summary. Neuro Oncol. 2021;23(8):1231-1251.

More free central nervous system questions

Sitting in February? Follow the twenty-week plan.

2,500+ cited questions like this one are waiting in the vault.

See plans and pricing