What is the indication for radiation therapy in a patient with carcinoma of the breast?

Indications for Radiation Therapy in Breast Cancer

Radiation therapy is indicated after breast-conserving surgery for invasive breast cancer and DCIS, after mastectomy in patients with ≥4 positive lymph nodes or tumors >5 cm, and should be strongly considered in patients with 1-3 positive nodes. 1

After Breast-Conserving Surgery (Lumpectomy)

Invasive Breast Cancer

• Whole-breast radiation is standard of care following lumpectomy for invasive breast cancer, reducing local recurrence by approximately 50-67% and improving breast cancer-specific survival 1, 2, 3
• Hypofractionated regimens (40.0-42.5 Gy in 15-16 fractions over 3-4 weeks) are now preferred over conventional fractionation (45-50 Gy in 25 fractions) for most patients, offering equivalent outcomes with better cosmesis and less toxicity 1
• A boost dose of 10-16 Gy to the tumor bed is recommended for high-risk patients: age <50 years, high-grade disease, or focally positive margins 1, 4

Ductal Carcinoma In Situ (DCIS)

• Standard whole-breast radiation (4,500-5,000 cGy at 180-200 cGy per fraction) is strongly recommended after breast-conserving surgery for DCIS, reducing local recurrence by 50-67% 2
• Radiation may be omitted in highly selected low-risk patients: tumor <10 mm, low/intermediate nuclear grade, adequate margins, and ER-positive status 2
• Radiation is NOT recommended following total mastectomy with clear margins for DCIS, as mastectomy alone is curative 2

Accelerated Partial Breast Irradiation (APBI)

• APBI is suitable for select patients ≥50 years with invasive ductal carcinoma ≤2 cm (T1), negative margins ≥2 mm, no lymphovascular invasion, ER-positive, and BRCA-negative 1
• For DCIS, APBI may be considered in low/intermediate grade, screen-detected tumors ≤2.5 cm with margins ≥3 mm 1

After Mastectomy (Post-Mastectomy Radiation Therapy)

Node-Positive Disease

• Chest wall and supraclavicular radiation is mandatory for patients with ≥4 positive axillary lymph nodes 1, 5
• For patients with 1-3 positive nodes, radiation should be strongly considered, particularly with tumors >5 cm or positive pathologic margins 1
• Strong consideration should be given to internal mammary node irradiation in node-positive patients (category 2B) 1, 5

Node-Negative Disease

• Chest wall radiation is recommended for primary tumors >5 cm or close/positive margins (<1 mm) 1
• Consider supraclavicular and internal mammary node radiation in patients with inadequate axillary evaluation or extensive lymphovascular invasion 1
• Radiation is NOT recommended for tumors ≤5 cm with margins ≥1 mm and negative nodes 1

Regional Nodal Irradiation

• Regional nodal irradiation (RNI) reduces locoregional recurrence, distant recurrence, and improves disease-free survival in node-positive patients, based on the NCIC-CTG MA.20 trial showing HR 0.68 for disease-free survival 1, 5
• RNI includes supraclavicular, infraclavicular, internal mammary nodes, and at-risk axillary regions 5
• Decisions regarding radiation should be based on pre-chemotherapy tumor characteristics, regardless of response to neoadjuvant therapy 1, 5

Technical Considerations

• CT-based treatment planning is mandatory to minimize cardiac and pulmonary exposure 1, 5
• Radiation should begin 2-4 weeks after uncomplicated surgery once adequate healing occurs 1, 2
• Hypofractionation is NOT recommended for post-mastectomy settings or when treating regional nodes 1
• Bolus should NOT be used during treatment 1, 6

Absolute Contraindications to Breast-Conserving Therapy with Radiation

• Previous moderate/high-dose radiation to the breast or chest wall 1
• Pregnancy requiring radiation during pregnancy 1
• Homozygous ATM mutation 1
• Diffuse suspicious/malignant microcalcifications that cannot be excised with satisfactory cosmesis 1
• Persistently positive pathologic margins after re-excision 1

Common Pitfalls

• Do NOT perform axillary lymph node dissection for pure DCIS—it is unnecessary and increases morbidity 2
• Do NOT combine axillary dissection with axillary radiation if invasion is found—this increases lymphedema risk to 40% 2
• Li-Fraumeni syndrome is a relative contraindication to radiation 1
• For left-sided lesions, minimize cardiac exposure in tangential fields 1