Phyllodes tumour of the breast is best classified histologically using the WHO criteria. Which feature is MOST closely linked to the designation 'malignant' rather than 'borderline'?
- A Stromal overgrowth defined as stroma without epithelium in ≥1 low-power (40×) field ✓
- B Pushing rather than infiltrative margins
- C Mild stromal cellularity with ≤4 mitoses per 10 HPF
- D Presence of heterologous elements alone
Correct answer: A. Stromal overgrowth defined as stroma without epithelium in ≥1 low-power (40×) field
Explanation
Stromal overgrowth — defined as presence of stroma devoid of epithelial elements in at least one low-power (4× objective, 40× total) field — is the single strongest predictor of malignant behaviour and distant metastasis in phyllodes tumours. Malignant phyllodes additionally shows marked stromal atypia, ≥10 mitoses/10 HPF, and infiltrative borders. Heterologous elements alone are insufficient without other malignant criteria.
Reference: Bailey & Love's Short Practice of Surgery, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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