[Histonet] impact of KOH on melanoma markers

[Gary Gracie]

Dear All

I recently received a request for HMB45, MART-1, MiTF, S100 and Tyrosinase on sections of toe nail. Our laboratory will usually soften the toe nail in Potassium hydroxide (KOH) either before processing or sometimes after trimming the paraffin block and floating the block in a jar of KOH.

The pathologist was reasonably certain the nail contained melanoma yet the markers were all negative or at best, weakly postive. Thankfully there was a second specimen that, for whatever reason, had missed the KOH treatment. This stained with the markers as expected.

Does anyone else use KOH for nail softening?

Has anyone ever encountered a problem with KOH "knocking out" epitopes as described?

Thanks

Gary Gracie
Senior Technical Officer
IHC Laboratory
Anatomical Pathology
St Vincents Hospital
Sydney, Australia

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