Real-world pregnancy outcomes following temporary interruption of adjuvant endocrine therapy in early-stage hormone receptor–positive breast cancer.

Abstract

e12702 Background: The POSITIVE trial established the feasibility of temporary interruption of adjuvant endocrine therapy (ET) to allow pregnancy in selected patients with hormone receptor–positive early breast cancer. However, trial populations may not fully reflect the demographic, racial, and treatment heterogeneity encountered in routine clinical practice. Real-world benchmarking of pregnancy outcomes following ET interruption remains limited. We evaluated pregnancy outcomes in a contemporary institutional cohort. Methods: We conducted a retrospective cohort study of patients with stage I–III hormone receptor–positive breast cancer who temporarily interrupted adjuvant ET for pregnancy intent between 1999–2023 at a tertiary academic cancer center. Patient demographics, tumor characteristics, treatment history, duration of ET prior to interruption, and pregnancy outcomes were abstracted. Descriptive statistics were used. Results: Among 94 eligible patients, the median age at diagnosis was 32 years (IQR 29–35). Most patients received prior chemotherapy (80%) and underwent mastectomy (66%). At ET interruption, 66% were receiving tamoxifen and 34% were receiving an aromatase inhibitor with ovarian suppression (AI/OFS). Median duration of ET prior to interruption was 28.7 months (IQR 14.7–42.8). Overall, 65.9% of patients achieved a successful pregnancy following ET interruption. Pregnancy success was higher in patients <35 compared with ≥35 (75.8% vs 46.9%, p = 0.01), and in White compared with Black patients (80% vs 47%, p = 0.03). Success rates were similar for patients receiving AI/OFS versus tamoxifen (71.9% vs 62.9%, p = 0.49). After delivery, 20.3% resumed ET. Prior live-birth rates at the time of ET interruption were identical in both the successful and failed pregnancy attempt groups (66%). The overall median time to follow up was 72 months. Median DFS was 73.6 months in the failed-pregnancy cohort and 68.6 months in the successful-pregnancy cohort, while overall survival did not differ between groups. Conclusions: In this diverse real-world cohort, pregnancy success following temporary endocrine therapy interruption was high and consistent with trial-reported outcomes. Younger age, White race, and higher parity were associated with higher pregnancy success, while overall survival remained comparable between groups. These findings support the feasibility of ET interruption for pregnancy attempts across a broader patient population. Larger cohort study is planned to compare outcomes to external controls who received uninterrupted endocrine therapy.