Partial-breast radiotherapy after breast conservation surgery for women with early breast cancer (UK IMPORT LOW): 10-year outcomes from a multicentre, open-label, randomised, controlled, phase 3, non-inferiority trial
Bibliographic record
Abstract
BACKGROUND: The IMPORT LOW trial evaluated partial-breast radiotherapy with intensity-modulated radiotherapy in women with early-stage breast cancer at below average risk of ipsilateral breast tumour recurrence (IBTR). 5-year results concluded non-inferiority of IBTR for reduced-dose and partial-breast radiotherapy, with similar or lower frequency of adverse effects compared with whole-breast radiotherapy. We report outcomes after 10 years. METHODS: IMPORT LOW was a randomised, open-label, multicentre, non-inferiority, phase 3 trial. Women were eligible if they were aged 50 years or older and had had breast conservation surgery for unifocal invasive ductal adenocarcinoma, pT1-2 (tumour size of ≤3 cm), N0-1 (none to three positive axillary nodes), grades 1-3, with microscopic margins of non-cancerous tissue of 2 mm or more. Patients were ineligible if they had a previous malignancy of any kind (except non-melanomatous skin cancer), had undergone mastectomy, or had received neoadjuvant or concurrent adjuvant chemotherapy. Patients were randomly assigned (1:1:1) by randomly permuted blocks to radiotherapy regimens of 40 Gy in 15 fractions to the whole breast (whole-breast group), 36 Gy in 15 fractions to the whole breast plus 40 Gy in 15 fractions to the partial breast (reduced-dose group), or 40 Gy in 15 fractions to the partial breast (partial-breast group). Participants were stratified by treatment centre, without masking. The primary endpoint was IBTR. 10-year outcomes were analysed in the intention-to-treat population. Clinician-reported late adverse effects were evaluated in all participants with available data analysed according to allocated treatment. The study is registered in the ISRCTN registry (ISRCTN12852634) and is now complete. FINDINGS: 2018 patients were recruited between May 3, 2007, and Oct 5, 2010, from 30 radiotherapy centres in the UK and randomly assigned to the whole-breast group (n=675), reduced-dose group (n=674), or partial-breast group (n=669). Two participants subsequently withdrew consent. Median age was 63 years (IQR 58-68). 854 (42%) of 2016 patients had grade 1 tumours, 959 (48%) had grade 2 tumours, and 200 (10%) had grade 3 tumours (three tumours were ungradable); 59 (3%) had node-positive disease. Median follow-up was 120 months (IQR 119-122) for the whole-breast group, 121 months (IQR 120-122) for the reduced-dose group, and 120 months (IQR 119-122) for the partial-breast group. By 10 years, IBTR events were reported for 45 of 2016 participants: 17 of 674 in the whole-breast group, 11 of 673 in the reduced-dose group, and 17 of 669 in the partial-breast group, with cumulative incidence of 2·8% (95% CI 1·8-4·5), 1·9% (1·1-3·5), and 3·0% (1·9-4·8), respectively. The estimated absolute difference in 10-year IBTR incidence was -1·02% (95% CI -1·98 to 0·99) for the reduced-dose group and 0·16% (-1·28 to 2·89) for the partial-breast group compared with the whole-breast group. Similar low levels of moderate or marked adverse effects were recorded for participants in all three groups in 10-year clinical assessments. Breast shrinkage had the highest incidence (30 [9%] of 321 in the whole-breast group, 28 [9%] of 322 in the reduced-dose group, and 22 [7%] of 333 in the partial-breast group). INTERPRETATION: Long-term follow-up provides further evidence that partial-breast and reduced-dose radiotherapy are as safe and effective as whole-breast radiotherapy in patients with low-risk early breast cancer. These results reaffirm the use of partial-breast radiotherapy delivered with intensity-modulated radiotherapy in this population as standard of care. FUNDING: Cancer Research UK.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.004 | 0.005 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.002 | 0.002 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.002 |
| Insufficient payload (model declined to judge) | 0.005 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".