Continued Preventive Effect of Radiotherapy After Breast-Conserving Surgery for DCIS in 20-Year Follow-Up of SweDCIS Trial
The 20-year follow-up of the Swedish randomized SweDCIS trial, reported by Wärnberg et al in the Journal of Clinical Oncology, shows a continued benefit of radiotherapy after breast-conserving surgery for ductal carcinoma in situ (DCIS) in preventing ipsilateral disease. A nonsignificant increase in contralateral breast disease was observed in the radiotherapy group.
Risk Reduction
In the trial, 1,046 women were randomly assigned to radiotherapy or not after breast-conserving surgery for primary DCIS between 1987 and 1999. Overall, there were 93 ipsilateral breast events in the radiotherapy group vs 165 in the control group; 20-year cumulative risk was 20.0% vs 32.0%, yielding an absolute risk reduction of 12.0% (95% confidence interval [CI] = 6.5–17.7) and relative risk reduction of 37.5%. Absolute risk reductions were 10.0% (95% CI = 6.0–14.0) for in situ and 2.0% (95% CI = −3.0 to 7.0) for invasive events, with relative risk reductions of 67.0% and 13.0%.
Contralateral Disease
There were 67 contralateral breast events in the radiotherapy group vs 48 in the control groups (hazard ratio [HR] = 1.38, 95% CI = 0.95–2.00), consisting of 11 vs 9 in situ events (HR = 1.2, 95% CI = 0.50–2.90) and 56 vs 39 invasive events (HR = 1.42, 95% CI = 0.94–2.14).
Disease-Specific and Overall Mortality
There were no differences between groups in 20-year breast cancer–specific death rates (4.1% vs 4.2%) or overall mortality (22.8% vs 27.0%). Of 21 women in the radiotherapy group who died from breast cancer, 18 actually received radiotherapy; of these, 9 developed an ipsilateral breast event before death. None of the 20 control group patients who died from breast cancer received radiotherapy outside of the study protocol. Among all 23 women who died from breast cancer without receiving postoperative radiotherapy, 17 developed an ipsilateral breast event.
Effect of Age
Younger women had a higher risk of invasive ipsilateral breast events and a smaller preventive effect of radiotherapy; hazard ratios for invasive disease for the radiotherapy vs control groups were 0.85 (95% CI = 0.51–1.47) in those aged < 52 years, 0.49 (95% CI = 0.25-0.98) in those aged 52 to 60 years, and 0.51 (95% CI = 0.27–0.97) in those aged ≥ 61 years.
The investigators concluded: “Use of adjuvant radiotherapy is supported by 20-year follow-up. Modest protection against invasive recurrences and a possible increase in contralateral cancers still call for a need to find groups of patients for whom radiotherapy could be avoided or mastectomy with breast reconstruction is indicated.”
Fredrik Wärnberg, MD, of Uppsala Academic Hospital, is the corresponding author for the Journal of Clinical Oncology article.
The study was supported by the Swedish Breast Cancer Association. Dr. Wärnberg receives research funding from Prelude.
The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.
