Background
Phase III non-inferiority randomized trial in 2,255 evaluable patients with higher-risk early breast cancer after lumpectomy and axillary surgery, comparing concurrent versus sequential tumor-bed boost during whole-breast irradiation (WBI). Concurrent boost shortens overall treatment time, but its impact on ipsilateral breast recurrence (IBR) and cosmesis vs the conventional sequential boost was unknown. Conducted at NRG Oncology / RTOG-affiliated sites. Enrollment May 2011 – June 2014.
Interventions and follow up
Arm A (concurrent): WBI 40 Gy in 15 fractions with an integrated concurrent boost of an additional 8 Gy in 15 fractions (0.53 Gy/day) using 3D-CRT or IMRT (n=1,137)
Arm B (sequential): WBI 50 Gy in 25 fractions or 42.7 Gy in 16 fractions, followed by a sequential boost of 12 Gy in 6 fractions or 14 Gy in 7 fractions (n=1,118)
Primary endpoint: Ipsilateral breast recurrence as first recurrence (non-inferiority margin: upper bound of 90% CI for HR ≤ 2.12)
mFollow up: 7.3 years
Arm B (sequential): WBI 50 Gy in 25 fractions or 42.7 Gy in 16 fractions, followed by a sequential boost of 12 Gy in 6 fractions or 14 Gy in 7 fractions (n=1,118)
Primary endpoint: Ipsilateral breast recurrence as first recurrence (non-inferiority margin: upper bound of 90% CI for HR ≤ 2.12)
mFollow up: 7.3 years
Results
5-year IBR: 2.1% (sequential) vs 1.9% (concurrent)
7-year IBR: 2.2% (sequential) vs 2.6% (concurrent)
IBR hazard ratio (concurrent vs sequential): 1.31 (90% CI 0.84–2.04; P=.037 for non-inferiority — non-inferiority criterion met)
Disease-free survival, overall survival, adverse events, and cosmetic outcomes: No differences observed between arms (numerical rates not reported in abstract)
7-year IBR: 2.2% (sequential) vs 2.6% (concurrent)
IBR hazard ratio (concurrent vs sequential): 1.31 (90% CI 0.84–2.04; P=.037 for non-inferiority — non-inferiority criterion met)
Disease-free survival, overall survival, adverse events, and cosmetic outcomes: No differences observed between arms (numerical rates not reported in abstract)
Adverse events
No differences in adverse events or cosmetic outcomes between arms; rates of grade ≥3 toxicity and detailed AE breakdown not reported in abstract.
Conclusions
A concurrent boost delivered during 15-fraction hypofractionated WBI is non-inferior to the conventional sequential boost for ipsilateral breast recurrence and produces equivalent cosmesis and toxicity, while shortening total treatment duration.
Key Limitations
Trial powered for non-inferiority of IBR; HR point estimate (1.31) favors sequential boost numerically, although the upper 90% CI remains below the prespecified margin; cosmetic and quality-of-life outcomes summarized rather than detailed in the abstract; long-term cosmesis beyond 7 years not yet reported.
Clinical Context
Supports adoption of a single 15-fraction regimen with integrated concurrent boost as an alternative to longer WBI-plus-sequential-boost schedules for patients at higher risk of IBR after breast-conserving surgery. Complements existing data on hypofractionation (START, Whelan, FAST-Forward) and on IMRT-based simultaneous integrated boost (e.g., RTOG 1005-style approaches and the IMPORT-HIGH trial), shortening treatment by ~1–2 weeks. Likely to influence ASTRO/ASCO whole-breast irradiation guidelines and is expected to accelerate uptake of simultaneous integrated boost in routine practice.