Comparative Effectiveness of Single Versus Dual Adjuvant Therapy After Breast-Conserving Surgery in Hormone Receptor-Positive Ductal Carcinoma In Situ: A Multicenter Retrospective Cohort Study

Background/Objectives: To evaluate the comparative effectiveness of single versus dual adjuvant treatment strategies for hormone receptor-positive (HR+) ductal carcinoma in situ (DCIS) following breast-conserving surgery (BCS). Methods: This was a multicenter, retrospective study. We retrospectively identified 645 patients with HR+ DCIS who underwent BCS between 2009 and 2020 from the Shanghai Jiao Tong University Breast Cancer Database (SJTU-BCDB). Patients were stratified according to adjuvant treatment regimens: BCS alone, BCS combined with radiotherapy (BCS + RT), BCS combined with endocrine therapy (BCS + ET), and BCS combined with radiotherapy and endocrine therapy (BCS + RT + ET). The primary endpoint was recurrence-free survival (RFS). Multivariable Cox regression and inverse probability of treatment weighting (IPTW) analyses were performed to evaluate treatment associations with RFS outcomes. Results: The median follow-up was 74.0 months. In multivariable Cox regression, compared with BCS + RT + ET, neither BCS + RT (HR, 0.62; 95% CI, 0.12–3.13; p = 0.564) nor BCS + ET (HR, 1.49; 95% CI, 0.43–5.11; p = 0.525) showed a statistically significant difference in RFS. IPTW-adjusted analyses similarly showed no statistically significant differences between BCS + RT and BCS + RT + ET (HR, 0.28; 95% CI, 0.06–1.44; p = 0.128) or between BCS + ET and BCS + RT + ET (HR, 1.82; 95% CI, 0.49–6.82; p = 0.373). Conclusions: Among patients with HR+ DCIS undergoing BCS, no statistically significant difference in RFS was observed between dual-modality and single-modality adjuvant therapy. However, the limited number of events and wide confidence intervals limit the precision of estimates regarding the incremental benefit of combined RT and ET. Larger prospective studies with adequate statistical power are warranted to further define the comparative effectiveness of these treatment strategies.