Which immunohistochemical marker supports epithelial origin and carcinomas?

• A. Vimentin
• B. Desmin
• C. Cytokeratins (e.g., CK AE1/AE3)
• D. GFAP

Answer: (C)

Cytokeratins are the intermediate filament proteins found in epithelial cells, so their presence by immunohistochemistry strongly supports an epithelial origin. In pathology, detecting cytokeratins with a broad-range antibody mix like AE1/AE3 helps confirm that a tumor is a carcinoma, since these tumors arise from epithelial tissue and typically express cytokeratins.

Other markers point to non-epithelial lineages: vimentin marks mesenchymal cells and many sarcomas; desmin is muscle-specific; GFAP marks glial cells. Those help distinguish non-epithelial tumors from carcinomas when immunoprofiles are ambiguous. Keep in mind that very poorly differentiated carcinomas can sometimes show variable cytokeratin expression, so a panel of markers and histologic context are used together for accurate classification.