Abstract
BackgroundRadiotherapy (RT) following breast-conserving surgery (BCS) for ductal carcinoma in situ (DCIS) reduces ipsilateral breast event rates in clinical trials. This study assessed the impact of DCIS treatment on a 20-year risk of ipsilateral DCIS (iDCIS) and ipsilateral invasive breast cancer (iIBC) in a population-based cohort.MethodsThe cohort comprised all women diagnosed with DCIS in the Netherlands during 1989–2004 with follow-up until 2017. Cumulative incidence of iDCIS and iIBC following BCS and BCS + RT were assessed. Associations of DCIS treatment with iDCIS and iIBC risk were estimated in multivariable Cox models.ResultsThe 20-year cumulative incidence of any ipsilateral breast event was 30.6% (95% confidence interval (CI): 28.9–32.6) after BCS compared to 18.2% (95% CI 16.3–20.3) following BCS + RT. Women treated with BCS compared to BCS + RT had higher risk of developing iDCIS and iIBC within 5 years after DCIS diagnosis (for iDCIS: hazard ratio (HR)age < 50 3.2 (95% CI 1.6–6.6); HRage ≥ 50 3.6 (95% CI 2.6–4.8) and for iIBC: HRage<50 2.1 (95% CI 1.4–3.2); HRage ≥ 50 4.3 (95% CI 3.0–6.0)). After 10 years, the risk of iDCIS and iIBC no longer differed for BCS versus BCS + RT (for iDCIS: HRage < 50 0.7 (95% CI 0.3–1.5); HRage ≥ 50 0.7 (95% CI 0.4–1.3) and for iIBC: HRage < 50 0.6 (95% CI 0.4–0.9); HRage ≥ 50 1.2 (95% CI 0.9–1.6)).ConclusionRT is associated with lower iDCIS and iIBC risk up to 10 years after BCS, but this effect wanes thereafter.
Highlights
Since the introduction of population-based mammography breast cancer screening in the 1990s, ductal carcinoma in situ (DCIS) comprises ~15% of all newly diagnosed neoplastic breast lesions [1, 2]
Women treated with breastconserving surgery (BCS) compared to BCS + RT had higher risk of developing ipsilateral DCIS (iDCIS) and ipsilateral IBC (iIBC) within 5 years after DCIS diagnosis (for iDCIS: hazard ratio (HR)age < 50 3.2; HRage ≥ 50 3.6 and for iIBC: HRage
After 10 years, the risk of iDCIS and iIBC no longer differed for BCS versus BCS + RT (for iDCIS: HRage < 50 0.7; HRage ≥ 50 0.7 and for iIBC: HRage < 50 0.6; HRage ≥ 50 1.2)
Summary
Since the introduction of population-based mammography breast cancer screening in the 1990s, ductal carcinoma in situ (DCIS) comprises ~15% of all newly diagnosed neoplastic breast lesions [1, 2]. RT as an adjunct to BCS as a treatment for DCIS was evaluated in several clinical trials (NSABP B17, EORTC 10853, SweDCIS, UK/ANZ), and a meta-analysis demonstrated a 15% absolute 10-year risk reduction of both subsequent ipsilateral DCIS (iDCIS) and ipsilateral IBC (iIBC) lesions for BCS + RT versus BCS only, without effect on breast cancer-specific survival and overall survival [5,6,7,8,9] How these trial data translate into a reduction of ipsilateral breast events in large, population-based patient cohorts in the longer term is unclear. CONCLUSION: RT is associated with lower iDCIS and iIBC risk up to 10 years after BCS, but this effect wanes thereafter
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