The sections show a moderately hypercellular glial tumour composed of astrocytic and oligodendroglial components. The astrocytic component is predominantly protoplasmic in type with a smaller component of fibrillary astrocytes. Both the astrocytic and oligodendroglial components show moderate nuclear pleomorphism. Moderate numbers of minigemistocytes and gliofibrillary oligodendrocytes are identified.
There is moderate mitotic activity and foci of microvascular proliferation with endothelial cell hyperplasia are noted in the oligodendroglial component. In addition a very small necrotic focus is seen in the oligodendroglial component. This incorporates thin-walled necrotic blood vessels.
- GFAP positive in astrocytic cells; negative in oligodendroglial cells. (not shown)
- Nogo-A positive in both astrocytic and oligodendroglialcells (not shown)
- Nestin positive
- IDH-1 positive
- p53 positive (not shown)
- p16 negative
- MGMT negative (likely methylated)
- Toposiomerase labelling index: Regional variation 2-10%
Despite the presence of a small necrotic focus in the oligodendroglioma component of this mixed oligoastrocytic tumour, a histopathological diagnosis of anaplastic oligoastrocytoma (WHO Grade III) is preferred to that of glioblastoma with an oligodendroglioma component (WHO Grade IV) because each component, in isolation, appears histologically of low grade, IDH-1 is mutated and the topoisomerase labelling index is low, certainly much lower than would be expected in glioblastoma with an oligodendroglioma component. In addition, MGMT is likely to be methylated which is an added positive prognostic indicator.
Chromosome 1p/19q deletion analysis might be considered to further characterize the tumour.
Brain tumour: High-grade anaplastic oligoastrocytoma favouring WHO Grade III.
NOTE: This case predates the 2016 WHO classification of CNS tumour revision. As no 1p19q co-deletion status is available a formal diagnosis cannot be reached and the NOS is therefore used (not otherwise specified) - which is recognised in the current classification for cases where molecular information is unavailable. It should also be noted, that under the new classification both an astrocytic and oligodendroglial component needs to be identified, each with its own molecular markers. True oligoastrocytomas are therefore going to be rare, and this case would most likely be classified as either an astrocytoma or an oligodendroglioma.