SAN DIEGO –
The follow-up analysis of the 2,016-subject IMPORT LOW study found that 10-year overall survival rates were 87.8% (95% confidence interval, 84.9-90.1) for a full-breast radiation group, 87.2% (95% CI, 84.3-89.6) for a reduced-dose group, and 90.3% (95% CI, 87.7-92.4) in a partial-breast group. Breast cancer radiotherapy specialist Anna Kirby, MB, MD (Res), MA, of the Royal Marsden and Institute of Cancer Research, London, reported the results at the annual meeting of the American Society for Radiation Oncology.
Ipsilateral breast tumor relapse was also similar in the three groups at the 10-year mark at 2.8% (95% CI, 1.8-4.5), 1.9% (95% CI, 1.1-3.4), and 2.8% (95% CI, 1.7-4.5), respectively. Moderate/marked adverse effects were deemed to be low.
Dr. Kirby said the new findings are not “practice-changing.” However, “this complementary data supporting the change in practice that happened in the UK and elsewhere following the publication back in 2017.”
The findings are “reassuring,” breast cancer radiology specialist Robert W. Mutter, MD, of the Mayo Clinic, Rochester, Minn., said in an interview after reviewing the study findings. While the outcomes and adverse events are similar between the groups, “partial-breast irradiation is attractive because it exposes less normal tissue such as the heart and lungs than whole-breast irradiation. This could lead to fewer side effects for patients later in life at a population level. Partial-breast irradiation should be considered a standard of care in selected patients.”
In a presentation at ASTRO, Dr. Kirby provided background about the motivation for the study. It was clear that radiotherapy reduces local recurrence by up to two-thirds in early breast cancer, she said. “But in a population with excellent prognosis, this translates into relatively small absolute benefits from radiotherapy for many of our lower-risk patients,” she said. “All patients treated are at risk of radiotherapy side effects, and these become the main hazard for many women. Radiotherapy that’s focused on the part of the breast that contained the tumor – the so-called tumor bed – may reduce the long-term complications from radiotherapy, particularly in the breast, and potentially in the heart and lung, whilst hopefully maintaining low local recurrence rates.”
The initial 5-year study was a randomized, multicenter, phase III trial of patients ≥ age 50 in the United Kingdom who were tracked since recruitment in 2007-2010 (median age, 63). All had undergone breast conservation surgery. The patients were assigned to the control group (n = 674, 40 Gy), reduced-dose (n = 673, 40 Gy) and partial-breast (n = 669, 40 Gy to partial breast only) in 15 daily treatment fractions. The initial results, published in The Lancet, reported noninferiority for both reduced-dose and partial-breast radiotherapy. Adverse effects were similar in the three groups except for change in breast appearance, which was better in partial-breast therapy vs. whole-breast, and breast harder or firmer, which was better in both partial- and reduced-dose groups vs. whole-breast.
Dr. Mutter described the IMPORT LOW trial as “a practice-changing study.”
The trial was unique since both the whole-breast and partial-breast arms received the same dosing schedule, he said, which “enables an unbiased assessment of the impact of target volume on treatment outcomes.” This contrasts “with other partial-breast irradiation studies where a different dosing schedule was employed for whole-breast and partial-breast irradiation.”
The new analysis tracked patients for a median of 121 months. “There is no difference in local recurrence rate across the three arms,” Dr. Kirby said. There were no differences in overall survival, breast cancer or cardiac deaths, she added, and “neither was there any difference in the time to any moderate or marked clinician-assessed breast normal tissue endpoint.”
Heart and lung outcomes may improve over time in the lower-dose groups because of less radiation exposure, “but we haven’t shown that yet with this data set.”
Dr. Mutter cautioned that “the results of this trial may not necessarily be extrapolated to other partial-breast irradiation techniques that treat a much smaller volume of breast tissue such as intracavitary brachytherapy and intraoperative radiotherapy. Whether these same excellent outcomes can be achieved with smaller treatment volumes is an area for further investigation.”
Funding information was not provided; the initial study was funded by Cancer Research UK. Dr. Kirby discloses travel costs paid by European Society of Radiotherapy and Oncology, and other authors have various disclosures including relationships with companies such as Pfizer, Seagen, AstraZeneca, Eli Lilly, Bayer, and Janssen. Dr. Mutter has no disclosures.