Breast cancer patients reported fewer moderate or marked side effects if they were treated with radiotherapy to part of the breast or a reduced dose to the whole breast, rather than with standard radiotherapy to the whole breast, according to a study presented at the 11th European Breast Cancer Conference.

The IMPORT LOW study of 2016 women in 41 centres in the UK has already shown that partial breast and reduced dose radiotherapy was as effective as whole breast radiotherapy in controlling cancer at five years, and women in the partial breast and reduced dose groups reported fewer side-effects, including less change in the appearance of the breast.

These latest results show that over half of patients in the study did not report moderate or marked side-effects at any point and that most side-effects reduced over time. The number of side-effects reported per person were fewer in the partial breast and reduced dose groups compared with the whole breast radiotherapy group.

Dr Indrani Bhattacharya, a clinical research fellow at the Institute of Cancer Research's Clinical Trials and Statistics Unit (London, UK), said, "This new information will help doctors discuss the risks and benefits of this type of radiotherapy with patients and may improve shared decision-making, as well as enabling them to tailor treatment for individual patients."

The IMPORT LOW study randomised women to receive standard radiotherapy at a dose of 40 Gy to the whole breast (the control group), or 36 Gy to the whole breast and 40 Gy to the part of the breast that contained the original tumour (reduced dose group), or 40 Gy only to the site of the original tumour (partial breast group).

The radiotherapy was given using hypofractionated intensity modulated radiotherapy (IMRT) – a technique that can deliver an even dose of radiation, minimizing the chances of hotspots of unwanted high doses and reducing the cosmetic problems that can occur after breast radiotherapy.

At the start of the study, after six months and one, two and five years after radiotherapy the women were asked about adverse side-effects, such as a hardening of tissue, pain, over-sensitivity of the treated area and build-up of fluid. Most of the side- effects reported by the women related to changes affecting the breast, and the commonest reported side-effect was "overall change in breast appearance".

"This new analysis shows that patients requiring whole breast radiotherapy can be reassured about the low risk of side-effects affecting the breast and body image. The technique of radiotherapy used in IMPORT LOW is easy to implement and deliver as the equipment and expertise is available in all centers worldwide."

The IMPORT LOW trial is the largest randomized trial to study the use of IMRT to deliver partial or low dose breast radiotherapy compared to whole breast radiotherapy, and has provided the largest complete set of patient-reported outcomes (PROMs) data for several points in time over five years.

"We know from this study and other studies that patients report more side-effects compared to doctors. This means that if we did not assess side-effects using PROMs, then the impact of the treatment-related side-effects on the patient may be underestimated," said Dr. Bhattacharya.

Isabel Rubio, director of the Breast Surgical Unit at Clinica Universidad de Navarra (Spain), commented, "These latest results from the IMPORT LOW trial provide important and reassuring information for clinicians and patients about side effects after partial or reduced dose radiotherapy, and will help them to make the best choices in each individual case."