ER, PR and HER2 results depend on how the tissue was handled before it reached the laboratory. Joint ASCO/CAP guidance for breast biomarker testing sets cold ischaemia time — from excision to immersion in fixative — at one hour or less, and fixation in 10% neutral buffered formalin for 6 to 72 hours.
Delayed fixation can lower ER and HER2 staining and produce false negatives, and under- or over-fixation affects both immunohistochemistry and in situ hybridisation. The pathologist can only interpret what the request form and container tell them.
- Ask theatres to record the time of excision and the time the specimen entered formalin.
- Aim for cold ischaemia time of one hour or less for breast specimens.
- Fix in 10% neutral buffered formalin for between 6 and 72 hours before processing.
- Note any deviation in the report when ER, PR or HER2 results are negative or equivocal.
- Consider repeat testing on another block or specimen when pre-analytical conditions were poor.
Why it matters
A false-negative ER or HER2 result can withhold effective treatment, and the error usually starts before the laboratory.
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