The Absolute Effect / Evidence / Breast Cancer
IMPORT HIGH
Clinical question: Can a simultaneous integrated boost shorten boost treatment while preserving ipsilateral breast tumour control?
Registry: ISRCTN47437448 · One underlying study; aliases and follow-up publications consolidated.
Phase III · randomized · non-inferiority · Evidence cut-off: 8 November 2026Design, population and eligibility
Multicentre, open-label randomized phase III non-inferiority trial of dose-escalated simultaneous integrated boost radiotherapy.
2,617 patients: 871 sequential-boost control, 874 48-Gy SIB, 872 53-Gy SIB.
Patients with early invasive breast cancer after breast-conserving surgery requiring whole-breast RT and tumour-bed boost.
Median follow-up 74 months; primary 5-year IBTR analysis.
Treatment and comparator
Intervention: Test 1: 36 Gy/15 fractions whole breast, 40 Gy/15 partial breast and 48 Gy/15 concomitant boost. Test 2: same whole/partial breast doses with 53 Gy/15 concomitant boost.
Comparator: 40 Gy/15 whole breast plus sequential 16 Gy/8 fractions photon boost.
Primary endpoint: Ipsilateral breast tumour relapse; non-inferiority margin ≤3% absolute excess at 5 years.
Key efficacy outcomes
5-year IBTR: 1.9% control; 2.0% 48-Gy SIB; 3.2% 53-Gy SIB
Absolute difference vs control: +0.1% (95% CI −0.8 to 1.7) for 48 Gy; +1.4% (0.03 to 3.8) for 53 Gy
Moderate/marked induration: 11.5%, 10.6%, 15.5% Control, 48-Gy and 53-Gy groups; 53-Gy vs control p=0.015.
The 48-Gy SIB met the prespecified non-inferiority criterion. The 53-Gy SIB did not: its upper confidence limit for absolute excess exceeded the 3% margin. Dose escalation increased induration.
Absolute outcome visualization
Five-year cumulative IBTR and moderate/marked breast induration.
Bars show source-reported endpoint values; no outcomes are reconstructed from median survival. Single-arm outcomes are not comparative effects.
NNT / NNH
No NNT: the 48-Gy regimen was evaluated for non-inferiority, not superiority. Absolute IBTR differences are small and confidence intervals include no difference.
No NNH is calculated for induration because the page reports incidence without a fully specified inferential comparison for all arms; the 53-Gy regimen had more moderate/marked induration (15.5% vs 11.5%, p=0.015).
Toxicity, grade 3–5 harms and treatment burden
Five-year clinician-reported moderate/marked breast induration: 11.5% control, 10.6% 48-Gy SIB (p=0.40 vs control), 15.5% 53-Gy SIB (p=0.015 vs control). No unsupported grade 3–5 toxicity rates are inferred.
SIB delivers the boost concurrently, avoiding the separate 8-fraction sequential boost. The 48-Gy schedule retains 15 treatment fractions; 53-Gy escalation increases breast induration without demonstrating better local control.
Quality of life
Patient-reported and photographic assessments were collected. No additional QoL advantage is claimed without a specific verified estimate.
Subgroups and applicability
The results concern early breast cancer after breast-conserving surgery. Boost selection should consider age, grade, margins, tumour-bed volume and individual recurrence risk.
Limitations
Open-label trial; relatively low IBTR event count; five-year primary endpoint; non-inferiority is specific to the 48-Gy schedule. The 53-Gy schedule failed NI.
Clinical interpretation
A 48-Gy/15-fraction simultaneous integrated boost is supported as non-inferior to sequential boost in the trial population. Escalating to 53 Gy/15 fractions is not supported and increases induration.
Contemporary-practice note (8 November 2026): historical trial efficacy is distinguished from present-day treatment selection. Comprehensive guideline-level freshness review remains pending for this batch; apply current disease-specific guidance and multidisciplinary context.
Primary sources and related publications
Missing values are not imputed; meeting abstracts are identified as such.