An unexpected negative immunostain is first a technical question. Check that the on-slide positive control stained appropriately, that the internal control cells in the section stained as they should, and that fixation and antigen retrieval were adequate, before concluding the tumour has lost the protein.
- Look at the external positive control first.
- Check internal control cells in the same section.
- Consider cold ischaemia time and fixation.
- Repeat on a different block if in doubt.
Why it matters
Reporting a technical failure as a biological loss can steer treatment wrongly.
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