MICROSCOPIC DESCRIPTION:
1&2. The sections show fragments of a moderately hypercellular glial tumour. This consists predominantly of moderately pleomorphic oligodendroglial cells arranged in diffuse sheets. These are admixed with a population of reactive astrocytes. Moderate numbers of gliofibrillary ligodendrocytes are also seen. Moderate numbers of mitotic figures are identified (4/10 HPF). There is also microvascular proliferation with multilayering of atypical cells around vessel lumena. No necrosis is seen.
IMMUNOHISTOCHEMISTRY:
- GFAP positive in reactive astrocytes and gliofibrillary oligodendrocytes; negative in tumour oligodendrocytes.
- NogoA positive in tumour oligodendrocytes.
- ATRX positive (not mutated)
- IDH-1 R132H positive (mutated)
- MGMT negative (likely methylated)
- p53 negative in tumour oligodendrocytes
- Topoisomerase labelling index: Approximately 10%
Note: 1p 19q co-deletion status has not been established but is implied by the non-mutated ATRX.
FINAL DIAGNOSIS: oligodendroglioma (WHO CNS grade 3).