A 55-year-old man has progressive sacral pain with a large midline destructive lesion on imaging. Biopsy shows cords of cells with abundant vacuolated bubbly cytoplasm embedded in a myxoid stroma. Which immunohistochemical marker is characteristic of this tumour?

• A Brachyury ✓
• B CD99
• C S-100 protein
• D WT1

Explanation

The findings describe chordoma, a malignant tumour derived from remnants of the primitive notochord, arising almost exclusively in the midline at the sacrococcygeal region or clivus. Histology shows physaliphorous cells, meaning bubbly vacuolated cells, in a myxoid matrix. Brachyury, a notochord transcription factor, is the sensitive and specific diagnostic marker. CD99 marks Ewing sarcoma and S-100 is shared with chondrosarcoma, which is the main mimic.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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