A 58-year-old man presents with months of intractable low back pain, saddle anaesthesia, and constipation. MRI shows a destructive midline presacral mass extending into the sacrum. Biopsy shows cords and nests of epithelioid cells embedded in abundant mucinous stroma, many cells containing multiple cytoplasmic vacuoles. The immunohistochemical marker specific for this tumour is:

• A S-100 protein
• B Desmin
• C CD34
• D Brachyury ✓

Explanation

The presentation is chordoma of the sacrum, a slow-growing malignant tumour derived from notochordal remnants, showing physaliphorous (bubble-bearing) vacuolated cells in a myxoid background. Brachyury, a transcription factor of notochordal differentiation, is the sensitive and relatively specific marker and distinguishes chordoma from its chief mimics. S-100 positivity also occurs in myxopapillary ependymoma and chondrosarcoma (the main differential for a sacral mass), so brachyury resolves that distinction.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.