Before a block is sent for next-generation sequencing, mark the tumour area on the H&E, estimate the proportion of tumour nuclei rather than tumour area, and record both on the request. Necrosis, mucin and dense inflammation inflate apparent tumour area without adding tumour DNA. Where content is borderline, macrodissection of the marked area is usually the simplest way to rescue the sample.
- Estimate tumour nuclei percentage, not tumour area.
- Mark the area to sample on the H&E slide.
- Exclude necrosis, mucin and heavy inflammation from the estimate.
- Record the estimate on the request form.
Why it matters
Most sequencing failures are decided at block selection, before the sample leaves the department.
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