Extended Endocrine Therapy Following 5 Years of Adjuvant Luteinizing Hormone-Releasing Hormone Agonist in Premenopausal Patients With Node-Positive, Hormone Receptor–Positive Breast Cancer: A Cohort Study

PURPOSE – To evaluate the clinical benefit of extended endocrine therapy (eET) after 5 years of adjuvant treatment with luteinizing hormone-releasing hormone agonists (LHRHa) in premenopausal women with node-positive, hormone receptor–positive early breast cancer (eBC).METHODS – We conducted a cohort study analysis on two prospectively collected data sets (the Young Women's Breast Cancer Study and IEO Breast Cancer Cohort). Eligible patients were diagnosed with eBC at age ≤40 years (between 2005 and 2016), had node-positive, hormone receptor–positive disease, and remained premenopausal after 5 years of adjuvant LHRHa with no evidence of recurrence. The primary end point was invasive breast cancer–free survival (IBCFS), calculated from the sixth year after the initiation of adjuvant endocrine therapy (ET; study baseline), and adjusted through the propensity score (PS) weighting analysis.RESULTS – A total of 501 patients were included in the analysis: 287 received eET for a median duration of 3.7 years (IQR, 2.3-5.0), including 48% tamoxifen monotherapy and 52% LHRHa plus tamoxifen or aromatase inhibitor. After a median follow-up of 7.3 years from the study baseline, the PS weighted IBCFS rates at 5 years were 85% in the eET group and 78% in the non-eET group (hazard ratio [HR], 0.63 [95% CI, 0.44 to 0.89]; P = .0135). The PS weighted distant recurrence-free survival rates at 5 years were 91% and 83% in the eET and non-eET group, respectively (cause-specific HR, 0.49 [95% CI, 0.31 to 0.79]). In both groups, bone fractures and major cardiovascular events were reported in 1% of patients.CONCLUSION – In this cohort study analysis, extending ET in premenopausal patients with node-positive eBC after 5 years of LHRHa treatment was associated with a clinically meaningful reduction in both invasive and distant breast cancer recurrences.