Do the guidelines exclude HER2 testing of cytology specimens (fluids and aspirates) that have been fixed in 95% ethanol rather than formalin?
Fixatives other than formalin are not precluded by the guidelines, which say “If laboratories choose to use alternative fixatives other than buffered formalin, the laboratory is obligated to validate that fixative’s performance against the results of testing of the same samples fixed also in buffered formalin and tested with the identical HER2 assay, and concordance in this situation must also be 95%.” Since cytology specimens are not ordinarily fixed in formalin, that sentence is not directly applicable, but labs performing HER2 testing on such specimens must document that they validated their methods and achieved acceptable concordance, in this case by comparing staining of alcohol fixed cytology specimens with routinely processed (formalin-fixed) tissue sections.
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