What are the indications for Accelerated Partial Breast Irradiation (APBI) in breast cancer?

Indications for Accelerated Partial Breast Irradiation (APBI) in Breast Cancer

APBI is an acceptable treatment option for patients with low risk for local recurrence, specifically those who are at least 50 years old, with unicentric, unifocal, node-negative, non-lobular breast cancer up to 3 cm without extensive intraductal components or vascular invasion, and with negative margins, especially if they will receive adjuvant endocrine treatment. 1

Patient Selection Criteria for APBI

Suitable Candidates:

• Age ≥60 years 1
• Not carriers of known BRCA1/2 mutations 1
• Treated with primary surgery for unifocal disease 1
• Stage I, ER-positive breast cancer 1
• Infiltrating ductal carcinoma or favorable histology 1
• No extensive intraductal component (EIC) or LCIS 1
• Negative surgical margins 1
• Tumor size ≤3 cm (ESMO guidelines) or T1N0 (NCCN guidelines) 1

Additional Considerations:

• APBI may also be considered for low-grade DCIS 1
• Non-lobular histology is preferred 1
• Adjuvant endocrine treatment enhances suitability 1

Treatment Delivery Methods and Dosing

Recommended Techniques:

• External beam radiation therapy: 38.5 Gy in 10 fractions delivered twice per day 1
• Brachytherapy: 34 Gy in 10 fractions delivered twice per day 1
• Both techniques should be delivered to the tumor bed 1

Treatment Schedule:

• Typically delivered over 5 days 2
• For external beam techniques, fractions should be separated by at least 6 hours 3

Efficacy and Outcomes

• APBI has demonstrated excellent local control rates in properly selected patients 2
• Five-year cumulative incidence rate of true recurrence is reported at 0.9% in prospective trials 2
• Cosmetic outcomes are generally good to excellent in approximately 95% of patients with >5 years follow-up 2

Important Caveats and Considerations

• APBI is still considered investigational by some guidelines, and patients should be encouraged to participate in high-quality prospective clinical trials when possible 1
• Intraoperative radiation therapy techniques (ELIOT, TARGIT) have shown significantly higher ipsilateral breast cancer recurrence rates compared to whole breast radiation therapy 1
• ASTRO stratification guidelines may not adequately predict ipsilateral breast tumor recurrences following APBI 1
• Follow-up data is still limited for some APBI techniques, and long-term results from several randomized trials are still awaited 1
• Whole breast irradiation remains the established standard with a longer track record of documented long-term effectiveness and safety 4

Clinical Decision Algorithm

1. Assess patient age (≥60 years preferred) 1
2. Confirm tumor characteristics:
   • Size ≤3 cm 1
   • Unifocal, unicentric disease 1
   • Node-negative status 1
   • Non-lobular histology 1
   • No extensive intraductal component or LCIS 1
3. Verify negative surgical margins (at least 2 mm) 5
4. Consider receptor status (ER-positive preferred) 1
5. Evaluate for presence of lymphovascular invasion (should be absent) 1
6. Determine if patient will receive adjuvant endocrine therapy (preferred) 1
7. Discuss BRCA mutation status (should be negative) 1

If all criteria are met, APBI can be offered as an alternative to whole breast irradiation.