Which immunohistochemical marker distinguishes primary peritoneal carcinoma from serosal mesothelioma on biopsy in a woman with diffuse peritoneal disease?
- A Calretinin positive, WT1 negative
- B PAX8 positive, calretinin negative ✓
- C CK5/6 positive, ER negative
- D Mesothelin positive, CA-125 negative
Correct answer: B. PAX8 positive, calretinin negative
Explanation
Primary peritoneal carcinoma (Mullerian origin, identical to high-grade serous ovarian carcinoma) is characterised immunohistochemically by positivity for PAX8 (Mullerian transcription factor), WT1, ER, and CA-125, and is negative for calretinin and CK5/6. Mesothelioma, in contrast, is positive for calretinin, CK5/6, and mesothelin and negative for PAX8. PAX8 positivity is the key differentiator for Mullerian-origin tumours.
Reference: Shaw's Textbook of Gynaecology, 17th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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