What are the radiotherapy guidelines for contouring in an adult female patient with a history of malignant or borderline malignant phyllodes breast tumor, who has undergone surgical resection with close or positive margins, in the adjuvant setting?

Radiotherapy Contouring Guidelines for Adjuvant Treatment of Phyllodes Breast Tumors

Direct Answer

For malignant or borderline phyllodes tumors with close (<5 mm) or positive margins after surgical resection, adjuvant radiotherapy should target the whole breast (after breast-conserving surgery) or chest wall (after mastectomy) to a dose of 50-60 Gy, using standard breast cancer radiotherapy contouring techniques without nodal irradiation. 1, 2, 3

Clinical Target Volume (CTV) Definition

After Breast-Conserving Surgery

• Contour the entire remaining breast tissue as the CTV, extending from the skin surface (excluding 5 mm skin flash) to the pectoralis major muscle posteriorly 4, 5
• Include the surgical bed with particular attention to areas of close or positive margins 1, 2
• Do NOT include axillary, supraclavicular, or internal mammary lymph nodes as phyllodes tumors rarely metastasize to lymph nodes (<1% nodal involvement) 3, 6

After Mastectomy

• Contour the entire chest wall from clavicle superiorly to inframammary fold inferiorly, and from midsternum medially to mid-axillary line laterally 1, 7
• Include the mastectomy scar with 1-2 cm margin 7
• Extend posteriorly to include the pectoralis major muscle and ribs 1
• Exclude axillary and supraclavicular nodal regions unless there is documented nodal involvement (extremely rare) 1, 6

Radiation Dose and Fractionation

• Standard dose: 50-60 Gy in 25-30 fractions (conventional fractionation) 5, 7
• Moderate dose-escalation to 60 Gy appears safe and effective for high-risk features 4, 5
• Hypofractionated regimens with biologically effective dose (BED) of approximately 90-103 Gy have shown excellent local control in recent series 4
• No boost to the tumor bed is routinely required, though may be considered for positive margins that cannot be re-excised 5

Indications for Adjuvant Radiotherapy

Malignant Phyllodes Tumors

Radiotherapy is strongly recommended for: 1, 2, 3

• Tumor size >5 cm (regardless of surgery type)
• Close margins (<5 mm) when re-excision is not feasible
• Positive margins when re-excision is not feasible
• Multifocal disease
• Recurrent disease
• Radiotherapy improves local control from 34-42% to 90-100% at 5 years, though does NOT improve overall survival 1, 8, 7

Borderline Phyllodes Tumors

Radiotherapy should be considered selectively for high-risk features: 1, 2

• Large tumors (>5 cm)
• Infiltrative margins
• Close or positive margins when clear margins cannot be achieved surgically despite re-excision attempts
• For borderline tumors with negative margins ≥1 cm, surgery alone is curative and radiotherapy is NOT indicated 2, 6

Benign Phyllodes Tumors

Radiotherapy is NOT indicated after margin-negative resection, as local control exceeds 85% with surgery alone 8

Critical Technical Considerations

Planning Target Volume (PTV)

• Add 5-10 mm margin to CTV for setup uncertainty and breathing motion 4
• Use deep inspiration breath-hold or respiratory gating for left-sided tumors to minimize cardiac dose 4

Organs at Risk

• Prioritize heart dose constraints (mean heart dose <4 Gy for left-sided lesions) 4
• Limit ipsilateral lung V20 <20% and mean lung dose <15 Gy 4
• Standard breast/chest wall radiotherapy constraints apply 4

Common Pitfalls to Avoid

• Do NOT contour regional lymph nodes (axillary, supraclavicular, internal mammary) as phyllodes tumors are sarcomas, not epithelial breast cancers, and nodal metastases are exceedingly rare 1, 3, 6
• Do NOT use breast cancer chemotherapy protocols or endocrine therapy as these have no proven efficacy in phyllodes tumors 3, 6
• Do NOT skip re-excision attempts if margins are close or positive and further surgery is feasible, as negative margins are the most important factor for local control 2, 3, 6
• Do NOT perform immediate reconstruction in high-risk malignant phyllodes tumors; delay reconstruction until after radiotherapy completion and when local recurrence risk has diminished (typically 2 years) 1, 2, 3

Evidence Quality and Nuances

The British Journal of Cancer 2025 guidelines provide the highest-quality framework, explicitly stating that radiotherapy improves local control but not survival in breast sarcomas including phyllodes tumors 1. This is corroborated by retrospective series showing 5-year local control improvement from 34-42% without radiotherapy to 90-100% with radiotherapy in borderline/malignant tumors 8, 7. The benefit is most pronounced after breast-conserving surgery with negative margins (100% vs 34% local control at 5 years), while the benefit after mastectomy is less clear (100% vs 83%, not statistically significant) 8. However, Asian series demonstrate benefit even after mastectomy for malignant phyllodes tumors 7.

Multidisciplinary Coordination

• All phyllodes tumors should be discussed at both breast cancer and sarcoma multidisciplinary team meetings to ensure appropriate risk stratification and treatment planning 1, 2, 6
• Pathology review at a specialist sarcoma center is recommended to confirm diagnosis and grade 2, 6