In the WHO grading system, what distinguishes anaplastic astrocytomas (grade III) from a low grade (glioma grade II)?
Presence of mitoses.
In the WHO grading system, what distinguishes anaplastic astrocytomas (grade III) from a gliblastoma (grade IV)
Absence of necrosis or microvascular proliferation / endothelial hyperplasia.
MICROSCOPIC DESCRIPTION: Paraffin sections show a densely hypercellular glial tumour with strong immunostaining for GFAP and nestin indicating astrocytic differentiation. There is moderate nuclear and cellular pleomorphism. Moderate numbers of mitotic figures are identified. Vessels are prominent throughout the tumour. These are enclosed within sleeves of fibrous tissue and do not show endothelial cell hyperplasia. No necrosis is seen. Moderate numbers of cells show strong immunostaining for synaptophysin. These are interpreted as incorporated pineocytes. No immunostaining for NeuN or IDH-1 is seen.
- 1p36 - No loss detected
- 19q13 - No loss detected
FINAL DIAGNOSIS: Anaplastic astrocytoma (WHO Grade III)
Note: Although this tumour is entirely consistent with IDH wild-type molecular subtype, strictly speaking, to conclusively establish this, IDH would need to be sequenced to ensure that a non-IDH1 R132H mutation was present. In practice, an IDH1 R132H negative tumour in an individual over 55-years-of-age makes the possibility of this being IDH mutant remote (<1%), and sequencing is not felt to be necessary by many institutions, and not recommended by the WHO classification of CNS tumours (2016).