Phyllodes tumours: the Refined Criteria upgraded half the borderlines without predicting spread

Design

Retrospective single-centre comparative clinicopathological study

Population

58 borderline or malignant phyllodes tumours, median follow-up 31.7 months

Primary outcome

Recurrence and distant metastasis by classification system

Effect

Mitoses ≥30/10 HPF (P = 0.005) and malignant heterologous elements (P < 0.001) predicted metastasis

This single-centre Brazilian series re-reviewed 62 phyllodes tumours diagnosed as borderline or malignant (2015–2025). Four were reclassified as benign; the remaining 58 (42 borderline, 16 malignant) were graded under WHO 2019, the Tan classification (2025) and the Refined Criteria (2023), and followed for a median of about 32 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 (P = 0.005) and malignant heterologous elements (P < 0.001) were independently associated with metastasis. The Tan system agreed with WHO in 97% of cases. The Refined Criteria moved 52% of borderline tumours into the malignant category, and none of those reclassified tumours metastasised during follow-up.

The practical point is that a broader definition of malignancy did not add prognostic information here, and the two features that did predict spread are ones every report should already capture. Follow-up was short for a tumour that can recur late, and the numbers are small, so this is not a reason to abandon any system — but it is a caution against upgrading on the Refined Criteria alone.

• Count stromal mitoses carefully in the most active area and report the number per 10 high-power fields.
• Sample generously; heterologous elements and mitotic hot spots are easily missed.
• Report malignant heterologous elements explicitly — they were strongly associated with metastasis.
• Be cautious about upgrading borderline tumours to malignant on the Refined Criteria alone.
• State which classification system was used in the report.

Why it matters

Calling a tumour malignant changes surgery and surveillance, so upgrading without prognostic gain has a cost.

Don't overread it

A small single-centre series with short follow-up — it does not establish that any classification system is wrong.

The statistics, in plain English

With only seven metastases, the study can identify strong predictors but not rule out weaker ones. 'None of the reclassified tumours metastasised' was observed over a median of 32 months; late events could still occur.

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