Effect of adjuvant endocrine therapy on recurrence and contralateral breast cancer in HR-positive DCIS after mastectomy

Abstract

Background: The clinical benefits of adjuvant endocrine therapy for patients with hormone receptor (HR)-positive ductal carcinoma in situ (DCIS) undergoing mastectomy remain controversial. While endocrine therapy is known to reduce recurrence after breast-conserving surgery, its role post-mastectomy is unclear. We aimed to assess the impact of adjuvant endocrine therapy on recurrence and contralateral breast cancer (CBC) in patients with HRpositive DCIS treated with mastectomy. Methods: In this retrospective multicenter cohort study, we included patients with HR-positive, pure DCIS who underwent mastectomy between 2003 and 2018 across three cancer centers in South Korea. Patients were stratified based on receipt of adjuvant endocrine therapy (ETx). Logistic regression and Cox proportional hazards models were used to evaluate associations between ETx and recurrence or CBC. Annual hazard rates were estimated using kernel-smoothed functions. Results: Of 1,186 eligible patients, 599 (50.5 %) received endocrine therapy. Median follow-up was 86.3 months. The recurrence rate was significantly lower in the ETx group compared to no-ETx (7.0 % vs. 11.7 %; OR, 0.57; p = 0.005). Locoregional recurrence was also lower (2.5 % vs. 4.8 %; OR, 0.51; p = 0.04). CBC occurred in 5.3 % overall, with a non-significant reduction in the ETx group (4.2 % vs. 6.5 %; OR, 0.63; p = 0.08). In multivariable Cox models, ETx was associated with reduced recurrence (HR, 0.53; p = 0.01) and CBC (HR, 0.53; p = 0.04). Risk reduction persisted beyond 10 years. Conclusion: Adjuvant endocrine therapy was associated with significant reductions in recurrence and CBC risk after mastectomy for HR-positive DCIS, supporting selective use based on individual risk assessment.