Effect of Radiotherapy After Breast-Conserving Surgery for Ductal Carcinoma in Situ: 20 Years Follow-Up in the Randomized SweDCIS Trial

Abstract

Four randomized studies show that adjuvant radiotherapy (RT) lowers the risk of subsequent ipsilateral breast events (IBEs) after breast-conserving surgery (BCS) for ductal carcinoma in situ (DCIS) by approximately 50% after 10 to 15 years. We present 20 years of follow-up data for the SweDCIS trial. Between 1987 and 1999 1,046 women were randomly assigned to RT or not after BCS for primary DCIS. Results up to 2005 have been published, and we now add another 7 years of follow-up. All breast cancer events and causes of death were registered. There were 129 in situ and 129 invasive IBEs. Absolute risk reduction in the RT arm was 12.0% at 20 years (95% CI, 6.5 to 17.7), with a relative risk reduction of 37.5%. Absolute reduction was 10.0% (95% CI, 6.0 to 14.0) for in situ and 2.0% (95% CI, -3.0 to 7.0) for invasive IBEs. There was a nonstatistically significantly increased number of contralateral events in the RT arm (67 v 48 events; hazard ratio, 1.38; 95% CI, 0.95 to 2.00). Breast cancer-specific death and overall survival were not influenced. Younger women experienced a relatively higher risk of invasive IBE and lower effect of RT. The hazard over time looked different for in situ and invasive IBEs. Use of adjuvant RT 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 RT could be avoided or mastectomy with breast reconstruction is indicated.