WHO classification of CNS tumours
=no grade 1 astrocytoma, IDH-mutant exists (only grades 2, 3, and 4 are available). Similarly, glioblastoma, IDH-wildtype can only ever be a grade 4 tumour
=example of conclusion: meningioma CNS WHO grade 1
=the term anaplastic is not currently used. what was previously known as an "anaplastic astrocytoma" is now referred to as an "astrocytoma, IDH-mutant, CNS WHO grade 3"
=the grading depends on the histological and molecular features. but If not compatible, the molecular features supersede the histologic features.
=It is important to note that a diagnosis can be reached without going through each of these steps. For example, 1p19q testing does not need necessarily need to be performed on every IDH positive tumour, especially if they have uniformly astrocytic morphology and clear-cut ATRX loss
=Incompleter tests for the final diagnosis (for example, imaging features with no histology, histology with no molecular)
Not elsewhere classified (NEC)
=complete tests that don't fit into a definite diagnosis (contradictory results)
Isocitrate dehydrogenase (IDH)
=IDH mutant positive >>>> ATRX>>>> intact with no mutation >>> oligodendroglioma
>>>> mutant >>>> astrocytoma (IDH mutant)
=In other words, ATRX status is on the reverse of 1p19q codeletion. in oligodendrogliomas (1p19q co deleted while intact non-mutated ATRX), astrocytoma (negative 1p19q co deleted while positive ATRX mutation)
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