An international group of breast pathologists has set out how stromal mitoses should be counted when grading phyllodes tumours as benign, borderline or malignant. Mitotic activity is central to that grading, but the method has never been clearly defined, which feeds disagreement between observers.
The group recommends counting in the most mitotically active area — the hotspot — rather than averaging across regions, and gives an operational protocol that converts counts to a standard area according to each microscope's field diameter. It also discusses digital tools for counting.
This is expert opinion rather than a validation study, but it addresses a practical source of inconsistency. Adopting one method across a department, and stating it in the report, makes grades more comparable between pathologists and over time.
- Count stromal mitoses in the most active hotspot when grading a phyllodes tumour.
- Convert counts to a standard area using your microscope's field diameter, not a fixed number of fields.
- State the counting method in the report so the grade can be interpreted and compared.
- Grade on mitoses together with the other histological criteria, not on mitoses alone.
Why it matters
Grade drives surgical margins and follow-up, and inconsistent mitotic counting is a common reason grades differ.
Don't overread it
An expert recommendation, not a study showing hotspot counting improves outcomes.
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