Which marker is NOT part of the immunohistochemistry panel for primary schwannomas?

• A. S100
• B. CD57 (Leu7)
• C. Epithelial Membrane Antigen
• D. GFAP

Answer: (C)

Schwannomas come from Schwann cells, so the immunohistochemistry panel focuses on markers that reflect neural crest–related differentiation. S100 protein is characteristically strongly positive in Schwann cells, which helps confirm a nerve sheath origin. GFAP can be variably positive, aligning with glial-type features sometimes seen in these tumors. CD57 (Leu7) can also be expressed in nerve sheath tumors, though its presence isn’t as definitive. Epithelial Membrane Antigen, however, is a marker typical of epithelial tumors and is strongly expressed in meningiomas, which helps distinguish them from schwannomas. Since schwannomas generally lack EMA staining, EMA is not included in the schwannoma-specific IHC panel. Therefore, Epithelial Membrane Antigen is the marker that’s not part of the panel.