1. Adjuvant radiotherapy reduced the risk of same-side recurrence following breast-conserving surgery for ductal carcinoma in situ (DCIS).
Evidence Rating Level: 1 (Excellent)
Study Rundown: The SweDCIS (Swedish Ductal Carcinoma in Situ) trial was a long-term randomized controlled trial that evaluated the effect of adjuvant radiotherapy (RT) following breast-conserving surgery for DCIS, and had previously demonstrated a reduced risk of local recurrence. The purpose of the present study was to analyze the 20 year survival results and to follow-up on earlier findings that suggested certain subgroups that might benefit from surgery without RT. Upon analysis, the authors confirmed that at 20 year follow-up, adjuvant RT reduced the risk of ipsilateral DCIS recurrence. However, they also noted that these patients had non-statistically significant increased risk of contralateral cancer. There was no difference in the rate of overall survival or breast cancer-specific mortality. Based on these results, the authors suggest that adjuvant RT reduces the risk of local recurrence, but further studies are required to identify patients who would not benefit from adjuvant RT.
In-Depth [randomized controlled trial]: This clinical trial ultimately included 1046 women who, after breast-conserving surgery, were randomly assigned to postoperative RT or to a control group. The primary end point was time to ipsilateral breast event (IBE). Secondary end points were overall survival, time to breast cancer death, and time to contralateral cancer. Median follow-up was 204 months. Upon survival analysis at 20 years, the cumulative risk of IBEs was 20% in the RT arm (95% CI, 16-24) and 32% in the control arm (95% CI, 28-36), with an absolute risk reduction of 12% (95% CI, 6.5-17.7) and relative risk reduction 37.5%. Cumulative breast cancer specific death was 4.1% (95% CI, 2.6-6.4) in the RT arm and 4.2% (95% CI, 2.7-6.5) in the control arm, while overall mortality was 22.8% (95% CI 19.1-27.3) in the RT arm and 27% (95% CI, 22.9-31.7) in the control arm. The hazard for in situ IBE was similar between the two arms after 12 years (approaching zero), as well as for invasive IBE after 10 years.
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