Age-specific survival after breast conservation versus mastectomy for ductal carcinoma in situ of the breast

Purpose Breast conservation for invasive breast cancer is associated with better survival and fewer complications than mastectomy, which is especially relevant for older patients. It is unclear whether this can be extrapolated to ductal carcinoma in situ (DCIS). Methods This population-based cohort study used data from the Breast Cancer Database Sweden (BCBaSe 3.0) to compare overall survival (OS), breast cancer–specific survival (BCSS) and local recurrence (LR) probabilities in three different age groups (< 60, 60–69, 70 + years) of women with primary DCIS undergoing breast-conserving surgery with radiotherapy (BCS + RT), mastectomy without radiotherapy (Mx-RT), or breast-conserving surgery without radiotherapy (BCS-RT) during 2008–2019. Complete cases (CC) and multiple imputation (MI) analyses were applied. Results In 7165 women, treatment was BCS + RT (53.3%), BCS-RT (13.4%), or Mx-RT (33.2%). Estimated 10-year OS was 90.4% (95% CI 89.3–91.5) and BCSS 98.8% (98.3–99.2). After adjustments for patient and tumour factors, including socioeconomic status and comorbidity, Mx-RT was associated with a higher overall mortality than BCS + RT in CC (HR 2.10; 95% CI 1.20–3.67) but not in MI analyses (HR 1.29; 0.95–1.76). In age 70 + years, however, the overall mortality was consistently increased (CC: HR 2.48; 1.09–5.62, MI: HR 1.89; 1.23–2.90). Also BCS-RT was associated with a higher overall mortality than BCS + RT (CC: HR 2.68; 1.34–5.34, and MI: HR 1.72; 1.23–2.39). The 10-year LR probability was low (7.2%, 95% CI 6.3-8.0). Compared to BCS + RT, Mx-RT was associated with a lower (HR 0.18, 95% CI 0.11–0.28) and BCS-RT with a higher LR risk (HR 1.79; 1.31–2.46), especially among ages 70+. Conclusion BCS + RT in DCIS appears safe. Acknowledging potential selection bias, BCS + RT may be associated with favourable overall survival outcomes in older women despite a higher risk of local recurrence.