The Absolute Effect / Evidence / ELIOT
ELIOT
In selected women with early breast cancer undergoing breast-conserving surgery, can single-dose electron intraoperative radiotherapy replace postoperative whole-breast irradiation?
Registry: NCT01849133 · One underlying randomized study; aliases and follow-up reports consolidated.
Design, population and eligibility
Single-centre, open-label, randomized phase III equivalence trial.
1,305 women; 654 assigned whole-breast irradiation and 651 ELIOT.
Women aged 48–75 years with unicentric tumour ≤25 mm and clinically negative axilla; final pathology may identify higher-risk features.
Median follow-up 12.4 years; 15-year local recurrence and OS reported.
Treatment and comparator
Electron intraoperative radiotherapy (ELIOT), 21 Gy single fraction delivered to the tumour bed during surgery.
Whole-breast irradiation, 50 Gy in 25 fractions plus a 10 Gy tumour-bed boost.
Primary endpoint: Ipsilateral breast tumour recurrence (IBTR); OS secondary.
Other endpoints: Local recurrence at 5, 10 and 15 years; overall survival.
Key efficacy results
Fifteen-year IBTR was 12.6% with ELIOT versus 2.4% with whole-breast irradiation; HR 4.62 (95% CI 2.68–7.95), P<0.0001.
Five-year IBTR: 4.2% versus 0.5%; ten-year: 8.1% versus 1.1%.
OS did not differ: HR 1.03 (95% CI 0.77–1.36), P=0.85; 15-year OS 83.4% versus 82.4%.
Source-reported outcome visualization
Fifteen-year ipsilateral breast tumour recurrence-free rate · 15 years
Calculated as 100% minus the source-reported 15-year IBTR cumulative incidence; clearly labelled as recurrence-free complements.
Absolute effect
Fifteen-year IBTR was 12.6% with ELIOT and 2.4% with whole-breast irradiation: absolute excess 10.2 percentage points. Approximate NNH ≈10 at 15 years for one additional IBTR with ELIOT compared with whole-breast irradiation. This is a recurrence endpoint, not a toxicity NNH.
NNT: No benefit NNT; ELIOT had more local recurrences.
NNH: Approximately 10 at 15 years for one additional ipsilateral breast tumour recurrence with ELIOT versus whole-breast irradiation.
Toxicity, harms and treatment burden
The principal harm is inferior local control; long-term adverse-event data were not collected in this trial, so late toxicity comparisons cannot be reliably quantified.
Single-session treatment reduces postoperative RT visits but does not eliminate the need for final pathology review or possible additional external-beam RT in patients with adverse features.
No grade 3–5 toxicity comparison or treatment-discontinuation rate is available in the final long-term abstract; do not invent one.
Quality of life and patient-reported outcomes
The single intraoperative treatment substantially reduces travel and treatment time, but the primary long-term publication does not provide a robust quantitative QoL comparison. Convenience should not obscure the 10.2-point 15-year local recurrence excess.
Subgroups, maturity and limitations
ELIOT is a single-centre trial with a specific electron technique and patient selection; external validity depends on expertise and pathology-based selection.
Local recurrence risk was markedly higher after ELIOT, particularly in patients with adverse pathological features in other analyses; risk-adapted selection is essential.
The trial did not collect long-term adverse-event data; absence of toxicity data is not evidence of absence of toxicity.
Clinical interpretation
Current-practice context · 1 November 2026 (full guideline freshness review pending): Intraoperative RT is not interchangeable with standard whole-breast RT for unselected early breast cancer. Where considered, use strict selection, discuss final pathology and the possibility of additional postoperative irradiation.
Primary sources and registry
Source hierarchy: primary randomized report and prespecified follow-up first. Missing numerical toxicity, discontinuation or QoL data are labelled rather than imputed.