What are the indications for radiotherapy in breast cancer?

Indications for Radiotherapy in Breast Cancer

Radiotherapy is strongly indicated after breast-conserving surgery for invasive breast cancer and DCIS, and after mastectomy for patients with ≥4 positive lymph nodes, T3-T4 tumors, or 1-3 positive nodes with high-risk features.

After Breast-Conserving Surgery (BCS)

Invasive Breast Cancer

• Whole-breast radiotherapy is mandatory after BCS for invasive disease 1, 2, 3
• Reduces local recurrence risk by two-thirds and improves overall survival 1
• Category 1 recommendation for node-positive disease 2

Exception: Women ≥70 years with stage pT1N0, ER-positive tumors, and clear margins (≥1 mm) may receive endocrine therapy alone without radiotherapy 1, 2, 1

Ductal Carcinoma In Situ (DCIS)

• Adjuvant breast irradiation decreases local recurrence by 50-60% but has no survival benefit 1, 3
• May be omitted in highly selected low-risk DCIS: tumor <10 mm, low/intermediate grade, margins >10 mm 1
• Tamoxifen should be considered with or without radiation for ER-positive DCIS 1

Boost Dose Considerations

• Strongly recommended for patients with: 4, 2
  • Age <50 years
  • Positive axillary nodes
  • Lymphovascular invasion
  • High-grade disease
  • Close or positive margins
• Typical boost dose: 10-16 Gy in 2 Gy fractions 3

After Mastectomy (Post-Mastectomy Radiotherapy - PMRT)

Absolute Indications

• ≥4 positive axillary lymph nodes - Category 1 1, 5, 3, 1, 6
• T3-T4 tumors regardless of nodal status 1, 3, 1
• Positive surgical margins 5, 7
• Tumors >5 cm 7

Strong Consideration (1-3 Positive Nodes)

PMRT should be strongly considered for patients with 1-3 positive nodes, particularly with additional risk factors 1, 5, 1, 8:

• Young age
• Grade 3 tumors
• Lymphovascular invasion
• ER/PR-negative status
• HER2-positive
• High proliferation (Ki-67)
• Central/medial tumor location with tumors >2 cm
• Limited axillary dissection (<10 nodes examined)

Node-Negative Disease

PMRT may be considered for 5, 8:

• Tumors >5 cm
• Positive or close margins (<1 mm)
• Central/medial tumors >2 cm with high-risk features (young age, extensive lymphovascular invasion)

Not recommended for node-negative, tumor ≤5 cm, margins ≥1 mm 5, 7

Regional Nodal Irradiation

After BCS or Mastectomy

Strongly recommended for 4, 2, 5:

• ≥4 positive nodes: Treat infraclavicular, supraclavicular areas, internal mammary nodes (Category 1)
• 1-3 positive nodes: Strong consideration for regional nodal irradiation (Category 2A/2B)
  • The MA.20 trial demonstrated improved disease-free survival (HR 0.68) and overall survival (HR 0.76) with regional nodal irradiation 2, 7

Internal Mammary Node Coverage

Indicated for 9, 5:

• Any axillary lymph node involvement
• Central or medial tumors
• Category 2B recommendation in most guidelines

After Neoadjuvant Systemic Therapy

Decision Based on Pre-Treatment Staging

PMRT indicated for 6, 10:

• Initial stage III-IV disease regardless of response
• Residual nodal disease at surgery (ypN1)
• Conditionally recommended for cT1-3N1 or cT3N0 with ypN0 after excellent response 6

After BCS Following Neoadjuvant Therapy

• Whole-breast irradiation is mandatory 10
• Decision should be based on pre-treatment characteristics, not post-treatment response 7

Radiation Technique and Dosing

Standard Fractionation

• Hypofractionation is preferred for whole-breast irradiation: 42.5 Gy in 16 fractions (2.66 Gy/fraction) 3, 11
• Conventional: 45-50 Gy in 25-28 fractions (1.8-2.0 Gy) 3
• Not recommended for post-mastectomy or regional nodal irradiation 11

Treatment Planning

• CT-based volumetric planning with 3D conformal RT required 6
• IMRT when 3D conformal cannot achieve treatment goals 6
• Deep inspiration breath-hold for cardiac sparing 6

Absolute Contraindications to Breast-Conserving Therapy with RT

• Previous moderate/high-dose chest wall radiation 4
• Pregnancy requiring radiation during pregnancy 4
• Diffuse suspicious/malignant microcalcifications 4
• Persistent positive margins after re-excision 4
• Inflammatory breast cancer 1
• Homozygous ATM mutation 11

Relative Contraindications

• Active connective tissue disease (scleroderma, lupus) 4
• Li-Fraumeni syndrome 11
• Tumors >5 cm in small breasts without neoadjuvant therapy 4

Key Pitfalls to Avoid

1. Do not omit RT after BCS based solely on favorable tumor biology—survival benefit is consistent across subtypes 1, 2
2. Do not use pre-treatment tumor size alone for PMRT decisions after neoadjuvant therapy—consider initial stage and residual nodal disease 7, 6
3. Do not routinely omit regional nodal irradiation in patients with 1-3 positive nodes—evidence supports benefit 2, 7
4. Ensure adequate margins: "no tumor on ink" for invasive cancer, 2 mm for DCIS 11