What are the indications for Post-Mastectomy Radiation Therapy (PMRT)?

Post-Mastectomy Radiation Therapy (PMRT) Indications

PMRT is mandatory for patients with ≥4 positive axillary lymph nodes and should be strongly considered for patients with 1-3 positive nodes when high-risk features are present. 1

Definitive Indications (Must Treat)

Four or More Positive Axillary Lymph Nodes

• PMRT is recommended for all patients with ≥4 positive axillary lymph nodes regardless of other factors 2, 1
• This provides clear survival benefit: 20-year breast cancer mortality reduces from 78.0% to 70.0% 1
• Treatment must include chest wall AND regional nodes (supraclavicular, infraclavicular, internal mammary nodes, and axillary apex) 1
• Supraclavicular field irradiation is specifically indicated given high failure rates in this nodal region 2, 1

T3-T4 Tumors

• PMRT is indicated for T3 tumors (>5 cm) with positive nodes 2
• PMRT is indicated for all T4 tumors independent of nodal status 2
• For node-negative T3 disease, chest wall irradiation with or without regional nodal irradiation is indicated 1

Positive or Close Surgical Margins

• PMRT should be administered for positive or close margins 1
• Chest wall irradiation is indicated in this setting 1

Strong Consideration (Risk-Stratified Approach)

One to Three Positive Lymph Nodes

• PMRT should be strongly considered using cumulative high-risk features 2, 1
• The 2015 ESMO guidelines now recommend routine use of PMRT for 1-3 positive nodes based on meta-analysis showing 20-year breast cancer mortality reduction from 49.4% to 41.5% 2, 1
• This represents an evolution from the 2001 ASCO guidelines which stated insufficient evidence for routine use 2

PMRT may be omitted when only a single low-risk feature exists:

• Age >45 years 1
• T1 tumor 1
• Single micrometastatic node 1
• Absence of lymphovascular invasion 1
• Favorable biology with excellent systemic therapy response 1

Additional risk factors favoring PMRT in 1-3 node-positive disease:

• Young age (<50 years) 2
• Vascular invasion 2
• Low number of examined axillary lymph nodes 2
• Grade 3 tumors 2
• Nodal metastasis >5 mm (particularly >10 mm) 3

Technical Specifications

Radiation Fields

• Regional nodal irradiation must include internal mammary nodes AND supraclavicular-axillary apical nodes in addition to chest wall 1
• After complete axillary dissection, the resected axilla should not be irradiated except for residual disease 2
• Full axillary radiotherapy should not be given routinely to patients undergoing complete or level I/II axillary dissection 2

Treatment Planning

• CT-based volumetric treatment planning with 3D conformal RT is mandatory 1
• IMRT should be used when 3D-CRT cannot achieve treatment goals 1
• Traditional doses: 45-50 Gy in 25-28 fractions 2
• Hypofractionation (15-16 fractions with 2.5-2.67 Gy) shows similar effectiveness 2

Special Scenarios

Neoadjuvant/Primary Systemic Therapy

• There is insufficient evidence to recommend PMRT for all patients treated with neoadjuvant therapy 2
• Decision should be based on pre-treatment staging and post-treatment pathologic findings 4

Positive Sentinel Node Without Completion Axillary Dissection

• PMRT should only be administered if other factors already independently justify its use (e.g., T3 tumor, multiple high-risk features) 1
• The positive sentinel node alone does not mandate PMRT without completion dissection 1

Critical Caveats

Concurrent Chemotherapy

• Doxorubicin must not be administered concurrently with PMRT due to toxicity concerns 1
• Sequencing of systemic therapy and radiation should be carefully planned 1

Cardiac and Pulmonary Toxicity

• Central lung distance should be kept ≤2.8 cm in tangential field technique or ≤1.4 cm in separate internal mammary field technique to minimize lung fibrosis 5
• Modern techniques with CT-based planning reduce cardiac mortality concerns seen in older trials 2