Multinational cohort study of survival impact of extended endocrine therapy for breast cancer subtypes in premenopausal patients

Premenopausal patients with node-positive, HR-positive, early breast cancer derive benefit from extended endocrine therapy (EET) following 5 years of LHRH agonist-based treatment. A cohort study in Italy and the United States evaluated the risk of invasive and distant recurrence across all surrogate breast cancer subtypes among patients with node-positive, HR-positive early breast cancer who remained premenopausal after 5 years of adjuvant therapy with a LHRH agonist who received or did not receive EET. Eligible patients were diagnosed with early breast cancer at 40 years of age or younger. In total, 487 patients were included; 276 received EET for a mediain duration of 3.7 years (IQR 2.2-5.0). Overall, 89 patients (18%) had luminal A-like disease, 298 (61%) had luminal B-like disease, and 100 (21%) had HER2-positive disease. The propensity score-weighted HR for invasive breast cancer-free survival comparing the EET with the no EET group was 0.68 (95% CI 0.32-1.45) in luminal A-like disease, 0.63 (0.40-1.00) in luminal B-like/HER2-negative disease, and 0.62 (0.21-1.87) in HER2-positive disease, with cause-specific PS-weighted HR for distant recurrence-free survival 0.25 (0.08-0.75), 0.54 (0.32-0.94) and 0.54 (0.12-2.53), respectively. The authors conclude that a lower risk wit EET use was observed across all surrogate breast cancer types, with the greatest effect among patients with lumina A-like disease.