Background
Phase III randomized non-inferiority trial (GEC-ESTRO). 1184 patients with low- or intermediate-risk early breast cancer (T1-2 ≤3cm, N0-1mi, M0) after BCS with clear margins. Multicatheter interstitial brachytherapy APBI (twice-daily fractions over 4–5 days) compared to whole-breast external beam RT. Brachytherapy delivers radiation precisely to the tumor bed via implanted catheters, sparing surrounding breast tissue.
Interventions and follow up
Arm A: Accelerated partial breast irradiation (APBI) via multicatheter interstitial brachytherapy: 32Gy in 8 fractions BID over 4–5 days (or 30.3Gy/7f BID)
Arm B: Whole-breast irradiation (WBI): 50Gy/25f or 50.4Gy/28f
Primary endpoint: Local recurrence-free interval (LRFI) — non-inferiority
mFollow up: 6.6 years
Arm B: Whole-breast irradiation (WBI): 50Gy/25f or 50.4Gy/28f
Primary endpoint: Local recurrence-free interval (LRFI) — non-inferiority
mFollow up: 6.6 years
Results
LRFI (5-yr): 98.3% vs 98.6% (APBI vs WBI) — non-inferior
IBTR (5-yr): 1.44% vs 0.92% — non-inferior (P=.042 for non-inferiority)
OS (5-yr): 97.3% vs 95.5% — similar
Distant DFS (5-yr): 97.5% vs 97.0% — similar
IBTR (5-yr): 1.44% vs 0.92% — non-inferior (P=.042 for non-inferiority)
OS (5-yr): 97.3% vs 95.5% — similar
Distant DFS (5-yr): 97.5% vs 97.0% — similar
Adverse events
Skin/soft tissue: late subcutaneous fibrosis 9.7% (APBI) vs 6.6% (WBI); telangiectasia 11.3% vs 5.8% (higher with APBI); fat necrosis 3.0% vs 2.6%
Breast symptoms: breast pain 13.1% vs 12.0% (similar)
Cosmesis: good/excellent at 5 years in 77% (APBI) vs 71% (WBI) — comparable
Breast symptoms: breast pain 13.1% vs 12.0% (similar)
Cosmesis: good/excellent at 5 years in 77% (APBI) vs 71% (WBI) — comparable
Conclusions
Multicatheter brachytherapy APBI was non-inferior to whole-breast RT for local recurrence in selected low-to-intermediate-risk early BC. Treatment time was dramatically reduced (4–5 days vs 5 weeks). GEC-ESTRO established brachytherapy APBI as an evidence-based alternative to WBI in appropriately selected patients.
Key Limitations
Multicatheter interstitial brachytherapy is technically demanding — requires specialized training, implant expertise, and afterloading equipment not universally available. The APBI group had slightly higher telangiectasia rates. Only low-to-intermediate-risk patients (grade 1–2, ≤3cm, pN0-1mi) were enrolled — high-risk features were excluded. This technique-intensive approach differs from external beam APBI (IMPORT LOW, RAPID) — results are not directly comparable. Long-term cardiac and contralateral breast cancer outcomes are not yet mature.
Clinical Context
GEC-ESTRO supports multicatheter brachytherapy APBI in selected low-risk early BC, endorsed by GEC-ESTRO/ESTRO guidelines and supported by ASTRO for suitable candidates. External beam APBI alternatives (IMPORT LOW, RAPID) are more accessible in most centers. ASTRO guidelines recommend APBI for patients ≥50 years with T1 invasive ductal carcinoma, pN0, ER+, no EIC, and margins ≥2mm. ESMO-MCBS: not applicable (RT non-inferiority trial).
References