Many predictive biomarker results depend on what happened to the tissue before it reached the bench. For breast cancer receptor testing, ASCO/CAP guidance asks for cold ischaemic time of one hour or less and fixation in 10% neutral buffered formalin for 6 to 72 hours. The same principles protect most immunohistochemistry and nucleic acid quality.
Under-fixation causes false-negative staining at the centre of the tissue; prolonged fixation degrades DNA and RNA. Record time out of the body and time into formalin on the request, and ask theatres and endoscopy units to supply it.
- Aim for cold ischaemic time of one hour or less
- Fix in 10% neutral buffered formalin for 6 to 72 hours for receptor studies
- Slice large resections promptly so formalin can penetrate
- Record collection and fixation times on the request form and in the report
Why it matters
A false-negative receptor or molecular result can deny a patient effective treatment.
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