Core Terms & Classification
WHO CNS5 (2021 classification)
WHO CNS5 is the 2021 fifth edition of the brain tumor classification, which for the first time integrates molecular markers into how gliomas are defined and graded.
In short: WHO CNS5 (2021 classification)
- It is the 2021 fifth edition of the WHO CNS tumor classification.
- It integrates molecular markers with traditional histology.
- It changed how gliomas are defined, named, and graded.
- It reflects a shift toward biology-based diagnosis.
What it is
WHO CNS5 is the fifth edition (published in 2021) of the WHO Classification of Tumors of the Central Nervous System. It marks a major change by integrating molecular (genetic) markers with the traditional microscope-based features to define and grade gliomas and other CNS tumors.
Understanding WHO CNS5 (2021 classification)
Building on the 2016 edition and on expert consensus work (cIMPACT-NOW), WHO CNS5 formally incorporated molecular findings into glioma diagnosis. For adult diffuse gliomas, this means classification now hinges on key markers — particularly IDH mutation status and 1p/19q codeletion — yielding three main groups: IDH-mutant astrocytoma, IDH-mutant and 1p/19q-codeleted oligodendroglioma, and IDH-wildtype glioblastoma. It also changed grading: certain molecular features can determine the grade regardless of how the tumor looks under the microscope (for example, a CDKN2A/B deletion can make an IDH-mutant astrocytoma grade 4). Grades are now written with Arabic numerals (1–4) within each tumor type. These changes make diagnosis more precise and biology-based. Understanding WHO CNS5 clarifies why modern glioma diagnosis depends so heavily on molecular testing.
Why it matters
Understanding WHO CNS5 helps patients and families see why molecular testing is now central to a glioma diagnosis — the 2021 system defines and grades these tumors by their biology, not just their appearance.
Common questions
What is WHO CNS5?
The 2021 fifth edition of the brain tumor classification.
What changed?
It integrates molecular markers into how gliomas are defined and graded.
Why does it matter?
Modern glioma diagnosis now depends heavily on molecular testing.
Bottom line
WHO CNS5 is the 2021 classification that integrates molecular markers into glioma diagnosis and grading, making the diagnosis more precise and biology-based.
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