High-Risk Features of Phyllodes Tumors
High-risk features of phyllodes tumors include tumor size >5 cm, infiltrative/positive margins, stromal overgrowth, marked stromal cellularity, high mitotic rate (≥10 mitoses per 10 high-power fields), and presence of necrosis—these features predict local recurrence and should trigger consideration of adjuvant radiotherapy. 1, 2, 3
Tumor Size Threshold
- Tumor size >5 cm is a critical high-risk feature that warrants consideration of adjuvant radiotherapy for both borderline and malignant phyllodes tumors 1, 2
- The British Journal of Cancer specifically identifies this 5 cm threshold as the point where radiotherapy demonstrates benefit for local control 1, 2
- In one study, tumor size ≥7 cm was uniformly present in patients who developed distant metastases 4
Margin Status and Tumor Borders
- Positive surgical margins significantly increase local recurrence risk (p=0.04 in univariate analysis) 4
- Close margins (<5 mm) are considered high-risk and should prompt re-excision attempts when feasible 1, 2
- Infiltrative tumor borders (as opposed to well-circumscribed borders) are associated with higher recurrence risk and should trigger consideration of adjuvant radiotherapy 1, 5
- All patients who experienced recurrence in one series had infiltrating tumor margins 5
Stromal Characteristics
- Marked stromal overgrowth is one of the most important predictors of both disease-free survival and cancer-specific survival (p<0.05) 3
- Stromal overgrowth was present in all but one patient who experienced recurrence in one series 5
- Marked stromal cellularity independently predicts worse disease-free and cancer-specific survival 3
Mitotic Activity
- High mitotic count (≥10 mitoses per 10 high-power fields) is a significant predictor of disease-free survival (p<0.05) 3
- This feature was uniformly present in patients who developed distant metastases 4
Presence of Necrosis
- Tumor necrosis is associated with a marked increase in local recurrence rates (p=0.006) 4
- Necrosis also predicts worse disease-free survival 3
- This feature was present in all patients who developed distant disease 4
Peritumoral Tissue Involvement
- Fibroproliferation in the surrounding breast tissue is strongly associated with increased local recurrence (p=0.001) 4
- Satellite nodules can occur even at previously negative margins in well-circumscribed borderline tumors, emphasizing the importance of wide margins 6
Clinical Implications of High-Risk Features
- When multiple aggressive features are present together (large size ≥7 cm, infiltrative borders, marked stromal overgrowth, marked cellularity, high mitotic count, and necrosis), the risk of distant metastases increases substantially—71% of patients with uniformly aggressive features developed distant disease 4
- Adjuvant radiotherapy should be strongly considered when high-risk features are present, particularly tumor size >5 cm, infiltrative margins, or inability to achieve clear margins despite re-excision 1, 2, 7
- Radiotherapy improves local control from 34-42% to 90-100% at 5 years, though it does not improve overall survival 1
Important Caveats
- Traditional histologic classification (benign vs. malignant) does not reliably predict local recurrence risk—benign and malignant tumors recurred at similar rates (21% vs. 18%) in one series 5
- The specific pathologic features listed above are more predictive than grade alone 4, 3
- Death from phyllodes tumors is rare (2%), and only tumors demonstrating uniformly aggressive pathologic features are associated with mortality 4