The sections show a densely hypercellular tumour. This is composed of a mixture of plump spindle and epithelioid cells arranged in intersecting fasciculi and diffuse sheets. Both cell types show moderate nuclear and cellular pleomorphism. Frequent mitotic figures are identified and there are large areas of confluent necrosis. At the interface between tumour and adjacent brain there is a prominent angiocentric pattern with tumour cells forming sleeves around blood vessels.
- GFAP positive in epithelioid tumour cells; negative in spindle cells
- EMA patchy strong positive staining in both spindle and epithelioid cells with perinuclear dot pattern in many cells
- Nestin positive - high
- ATRX positive (not mutated)
- IDH-1 R 132H negative (not mutated)
- MGMT negative (likely methylated)
- Cytokeratins CK7, CK20, CK5&6, AE1/AE3 all negative
- CDX2 negative
- SMA positive in blood vessels; negative in tumour cells
- Desmin patchy moderate staining in spindle cells
- Topoisomerase labelling index: Approximately 35%. Immunostaining present in nuclei of both spindle and epithelioid cells.
DIAGNOSIS: "Brain tumour": Gliosarcoma (WHO Grade IV)
COMMENT: The presence of perinuclear dot immunostaining for epithelial membrane antigen (EMA) suggests that this gliosarcoma may have arisen in an anaplastic ependymoma. Otherwise the histopathological and immunohistochemistry features are those of conventional gliosarcoma.