Abstract PS3-07-09: Extended Endocrine Therapy (eET) Following Five Years of Adjuvant LHRH-agonist (LHRHa) in Premenopausal Patients with Node-Positive, Hormone Receptor (HR)-Positive early Breast Cancer (eBC): a subanalysis according to surrogate subtypes

Abstract Background: In a previous cohort study analysis on 503 patients with node-positive early breast cancer (eBC) who remained premenopausal after 5 years of LHRHa treatment, we showed that the extension of endocrine therapy (ET) either with tamoxifen alone or by continuing previous LHRHa was associated with reduced invasive and distant breast cancer recurrences (Valenza, ASCO 2025). Due to the relative higher incidence of long-term recurrences in patients with luminal A-like eBC, the benefit of eET may differ according to surrogate breast cancer subtypes. Methods: We conducted a cohort study on two ongoing prospective datasets (Young Women's Study and European Institute of Oncology's Breast Cancer Dataset) to evaluate the clinical benefit of eET in women who had completed 5 years of adjuvant LHRHa, remained premenopausal and had no evidence of distant or locoregional recurrence. This study included women