Gross pathology
Sacral mass: multiple brown/tan core fragments measuring 0.2 to 1.6 cm
Microscopic evaluation
Immunohistochemistry stains for pancytokeratin, GCDFP-15, SATB-2, Ki67, P63, and SOX-10 were utilised with adequate control in the evaluation of the biopsy.
Pancytokeratin, GCDFP-15, and SOX-10 are negative. SATB-2 and P63 are positive. The Ki67 proliferation index is significantly up to 25%.
The morphologic features and the immunohistochemical staining pattern support the diagnosis of a giant cell tumour of the bone.
An additional immunohistochemical stain shows nuclear positivity of the neoplastic cells for H3G34W, supporting the diagnosis.