Thousands of women who undergo radiotherapy for low-risk breast cancer could be spared some of the side effects of treatment after a study confirmed that more targeted treatments are just as effective at controlling the disease in the long term.
The IMPORT LOW trial has transformed how we treat early breast cancer, offering women a safer and effective option while significantly reducing some side effects
Charlotte Coles
Findings of the IMPORT LOW trial, led by researchers at the University of Cambridge and The Institute of Cancer Research, London, showed that limiting radiation to only the tumour area is just as effective as treating the whole breast, therefore reducing radiation exposure.
At the 10-year follow-up mark, the team showed that recurrence rates for the less aggressive technique - known as partial breast radiotherapy - were 3 per cent, the same as for whole breast radiotherapy, according to findings published in The Lancet Oncology.
Partial breast radiotherapy, which has been shown to reduce long-term changes in breast appearance, has now been adopted widely across the NHS and internationally.
It is hoped that more than 9,000 women a year in the UK - one in four patients who require radiotherapy for breast cancer - will benefit from the more personalised treatment, along with many tens of thousands of patients around the world.
More than 37,000 women have radiotherapy for breast cancer in the UK each year. The procedure is given after a tumour is surgically removed and is aimed at eradicating all remaining cancer cells.
Side effects of radiotherapy include changes in breast size or shape, swelling in the arm or breast due to fluid build-up, as well as pain or breast hardness.
IMPORT LOW was co-led by Professor Charlotte Coles from the University of Cambridge and Cambridge University Hospitals NHS Foundation Trust, and Professor Judith Bliss, Founding Director of The Institute of Cancer Research Clinical Trials and Statistics Unit (ICR-CTSU).
Professor Coles, Chief Investigator of the study, said: "The IMPORT LOW trial has transformed how we treat early breast cancer, offering women a safer and effective option while significantly reducing some side effects. By targeting the area around the tumour, rather than the whole breast, we have demonstrated that patients can achieve the same outstanding long-term outcomes with fewer complications.
"This approach is now widely adopted across the NHS, sparing thousands of women from unnecessary radiation exposure. The results of this study have not only shaped UK clinical practice but also informed international guidelines, ensuring that women worldwide benefit from this personalised, evidence-based treatment."
The IMPORT LOW trial, which was managed by the ICR-CTSU and funded by Cancer Research UK, compared three radiotherapy approaches: whole-breast radiotherapy, partial-breast radiotherapy and partial-breast radiotherapy with reduced-dose to the part of the breast that was distant from the primary cancer. It involved more than 2,000 women at 30 radiotherapy centres in the UK who were monitored for 10 years after treatment.
The researchers found no difference in rates of cancer recurrence with either of the less aggressive approaches, and patients reported significantly lower side-effects.
Patients who received partial-breast radiotherapy were significantly less likely to experience long-term changes in breast appearance. Only 15 per cent of patients reported noticeable changes at five years, compared to 27 per cent in the whole-breast group.
Experts estimate that between 25-30 per cent of patients who have radiotherapy treatment for breast cancer are eligible for partial breast radiotherapy, due to their cancer being low risk and, to date, around 74,000 women have benefitted from the gentler technique.
Following the trial's success, partial-breast radiotherapy has been integrated into NHS treatment guidelines and endorsed by the Royal College of Radiologists and Association of Breast Surgery. The IMPORT LOW trial has also changed clinical practice worldwide, informing the 2022 European Society of Radiation Oncology guidelines, and 2023 American Society of Radiotherapy and Oncology (ASTRO) partial breast irradiation guidelines.
Since 2020, partial breast radiotherapy has been carried out in five sessions of radiotherapy instead of 15 - making it cheaper for the NHS and less burdensome for patients.
First author Dr Anna Kirby from The Royal Marsden NHS Foundation Trust and The Institute of Cancer Research said: "The long-term results of this study confirm that a less aggressive approach - limiting radiotherapy to the part of the breast where the tumour was - is just as effective as traditional whole-breast radiotherapy. Patients receiving partial breast radiotherapy experience fewer side effects while maintaining excellent cancer control."
Dr Fay Cafferty, also from The Institute of Cancer Research, said: "This latest analysis confirms that partial breast radiotherapy remains a safe and effective treatment option, supporting its continued adoption as the standard of care in the UK and globally. Along with the parallel reduction in the number of radiotherapy sessions now required, the approach provides significant advantages both for patients and healthcare systems, helping to optimise resources while ensuring excellent long-term cancer control."
The study was supported by the National Institute for Health and Care Research's Biomedical Research Centres in Cambridge and at the Royal Marsden and The Institute of Cancer Research.
Dr Dani Edmunds, Research Information Manager at Cancer Research UK, said: "This study shows that we can safely reduce the amount of radiotherapy we give to many women with early breast cancer without increasing the risk of the disease coming back.
"This means people experience fewer long-term side effects, like changes in how their breasts look or feel, making the treatment kinder."
Reference
Kirby, AM et al. 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. Lancet Oncology; July 2025; DOI: 10.1016/S1470-2045(25)00194-9
