- Design
- Retrospective clinicopathological comparison of three classification systems
- Population
- 58 borderline or malignant phyllodes tumours of the breast
- Primary outcome
- Recurrence and metastasis by histological feature and classification
- Effect
- Mitoses ≥30/10 HPF (P = 0.005) and heterologous elements (P < 0.001) linked to metastasis
Pathologists re-reviewed 58 borderline (42) and malignant (16) phyllodes tumours of the breast diagnosed between 2015 and 2025 and classified each by WHO 2019, the Tan system (2025) and the Refined Criteria (2023). Median follow-up was 31.7 months.
Six borderline tumours recurred locally without metastasis. Seven malignant tumours metastasised and two patients died of disease. Stromal mitoses of 30 or more per 10 high-power fields and malignant heterologous elements were independently associated with metastasis. The Tan system agreed with WHO 2019 in 97% of cases. The Refined Criteria upgraded 52% of borderline tumours to malignant, and none of those upgraded tumours metastasised during follow-up.
With few events and modest follow-up, this cannot settle which system is best. But it does not support adopting criteria that label many more tumours malignant without better prediction.
The practical emphasis is on two features worth stating explicitly in every report, and on sampling thoroughly enough to find them.
- Report stromal mitotic count per 10 HPF explicitly.
- State whether malignant heterologous elements are present.
- Continue to use WHO 2019 grading; alternative systems did not improve prediction here.
- Sample the tumour extensively before assigning a borderline grade.
Why it matters
Over-calling borderline phyllodes as malignant can drive more surgery and adjuvant treatment without better prediction.
Don't overread it
Few metastatic events and under three years of follow-up limit the comparison between systems.
The statistics, in plain English
With only seven metastases, each classification system is being judged on a handful of events. That none of the 22 or so upgraded tumours metastasised suggests over-calling, but longer follow-up could change it.
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