Diffuse astrocytoma NOS
Updates to Freetext Attributes
The patient proceeded to surgery.
Histopathology
MICROSCOPIC DESCRIPTION: Paraffin sections show a moderately hypercellular glial tumour. The majority of tumour cells have oligodendroglial morphological features with moderately pleomorphic round and oval hyperchromatic nuclei and a paucity of delicate processes. Moderate numbers of mini-gemistocytes and gliofibrillary oligodendroglial cells are also noted. There is prominent microcyst formation. Scattered mitotic figures are noted (2 in 20 HPF). There is no microvascular proliferation and no necrosis is identified. The features are of a diffuse glioma favouring oligodendroglioma (WHO Grade II).
IMMUNOHISTOCHEMISTRY:
- GFAP positive
- Nestin positive (low)
- Nogo A negative
- IDH-1 R132H negative (not mutated)
- ATRX negative (mutated)
- p53 positive
- MGMT negative (likely methylated)
- p16 CDKN2A positive
- Topoisomerase labelling index: Approximately 2%.
FINAL DIAGNOSIS: probable IDH wild type diffuse astrocytoma (WHO Grade II).
Note: The diagnosis of astrocytoma is very likely but according to the current WHO classification of CNS tumours (2016) it has actually not yet been established in this case as the IDH wild-type status has only been inferred with a negative IDH1 R132H immunohistochemistry. Although it is likely to reflect true IDH wild-type status, it is possible that this is a non-R132H IDH1 mutation or an IDH2 mutation (which account for ~20% of all IDH mutations). In younger patients, IDH sequencing is therefore recommended to prove that no IDH mutation is present.
Additionally, as the histological morphology suggests that this is an oligodendroglioma, 1p19q codeletion status would also need to be established (if IDH sequencing showed a mutation).
Having said that the absence of IDH1-R132H and mutated ATRX are highly suggestive of 1p19q being intact, and thus not an oligodendroglioma under the current classification.
Overall this would be therefore classified as a diffuse astrocytoma NOS.
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