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.