- Design
- Retrospective single-institution clinicopathological comparison
- Population
- 58 borderline or malignant breast phyllodes tumours
- Primary outcome
- Recurrence and metastasis by classification system
- Effect
- Refined Criteria upgraded 52% of borderline; none metastasised; mitoses ≥30/10 HPF P = .005
This single-institution series reclassified 58 borderline or malignant phyllodes tumours (42 borderline, 16 malignant) under the WHO 2019 criteria, a 2025 alternative system and the 2023 Refined Criteria. Median follow-up was about 32 months.
Six borderline tumours recurred locally, none metastasised. Seven malignant tumours metastasised and two patients died. High stromal mitotic activity (30 or more per 10 high-power fields) and malignant heterologous elements were independently associated with metastasis. The 2025 system agreed with WHO in 97% of cases, while the Refined Criteria moved 52% of borderline tumours to malignant — none of which metastasised in follow-up.
For reporting, this supports continuing with WHO criteria and paying particular attention to mitotic count and heterologous elements, which require adequate sampling. A series of 58 tumours with under three years' follow-up cannot settle the question, but it argues against adopting broader criteria that may overtreat.
- Count stromal mitoses carefully in phyllodes tumours; 30 or more per 10 high-power fields was linked to metastasis.
- Sample generously to find malignant heterologous elements, which carried the strongest association.
- Continue grading with WHO criteria; the Refined Criteria upgraded many tumours without prognostic gain here.
- Flag limited sampling in the report when grade could be affected.
Why it matters
A broader definition of malignancy changes surgical margins and surveillance for many women without clear benefit.
Don't overread it
This is one centre, 58 tumours and about 32 months' follow-up; later metastases in upgraded tumours cannot be excluded.
The statistics, in plain English
With only seven metastases, any association is based on few events, and P values here say the link is unlikely to be chance but not how strong it is. Short follow-up may miss later metastases in the reclassified tumours.
Read the rest in the app
You have read your two free briefings this month. The app carries all 27 specialties, every morning, free — and this finding is waiting in it.
Scan to keep reading on your phone. No account needed to start.
Tomorrow morning, before your first patient
One edition a day for pathology, written by the desk, every claim tied to its paper. Six minutes.
Get the app — free