Real-world data on neoadjuvant endocrine therapy in ER-positive/HER2-negative breast cancer.

PURPOSE: Neoadjuvant endocrine therapy (NET) has been shown to be effective in ER-positive/HER2-negative breast cancer in clinical trials. However, adoption in clinical practice is still limited. Real-world data may provide useful insights into effectiveness, toxicities and quality of care, potentially rendering clinical trial results to the real-world setting. Our purpose was to report real-world data of a cohort of postmenopausal patients submitted to NET. METHODS: This prospective cohort study evaluated 146 postmenopausal female patients with ER-positive/HER2-negative breast cancer treated with NET at three tertiary hospitals between 2016 and 2018. Clinicopathological information were collected prospectively. Preoperative Endocrine Prognostic Index (PEPI) score was calculated for tumors submitted to at least 16 weeks of NET. RESULTS: Median age was 67 years old, and 87.8% had stage I-II disease. Most tumors had histological grade II (76.1%). Median pretreatment Ki67 expression was 10%. Aromatase inhibitor was used in 99.5% of patients, and median treatment duration was 21.0 weeks. No tumor progressed during NET. Breast-conserving surgery was performed in the majority of patients (63.0%), as well as sentinel lymph-node biopsy (76.7%). Pathological complete response rate was 1.0%. 43 patients (29.5%) had PEPI score 0, and 26% had PEPI scores 4-5. Posttreatment Ki67 median expression was 3.0%, and only five tumors (3.4%) showed marked increase in Ki67 expression during treatment. Seven patients (4.8%) had HER2-positive residual disease, and were treated with adjuvant chemotherapy plus trastuzumab. CONCLUSIONS: Our real-world data shows that NET is effective and safe in postmenopausal patients with ER-positive/HER2-negative breast cancer. Postmenopausal status and low-risk luminal tumor features (luminal A-like) should be used as selection criteria to ensure the best results with NET.