BackgroundMonthly goserelin 3.6 mg dosing suppresses estradiol (E2) production and has proven efficacy in pre-menopausal women with estrogen receptor (ER)-positive breast cancer. This non-inferiority study evaluated the efficacy and safety of 3-monthly goserelin 10.8 mg compared with monthly goserelin 3.6 mg.MethodsThis was a Phase 3, open-label, multicenter trial. Pre-menopausal women with ER-positive advanced breast cancer were randomized to 3-monthly goserelin 10.8 mg or monthly goserelin 3.6 mg; all patients received concomitant tamoxifen (20 mg daily). The primary endpoint was progression-free survival (PFS) rate at 24 weeks; non-inferiority was to be confirmed if the entire 95 % confidence interval (CI) for the treatment difference was above −17.5 %. Secondary endpoints included objective response rate (ORR), serum E2 levels, safety, and tolerability.ResultsIn total, 222 patients were randomized (goserelin 10.8 mg, n = 109; goserelin 3.6 mg, n = 113). PFS rate at week 24 was 61.5 % (goserelin 10.8 mg) and 60.2 % (goserelin 3.6 mg); treatment difference (95 % CI) was 1.3 % (−11.4, 13.9), confirming non-inferiority of goserelin 10.8 mg compared with goserelin 3.6 mg. ORR was 23.9 % (goserelin 10.8 mg) and 26.9 % (goserelin 3.6 mg); treatment difference (95 % CI) was −3.0 % (−15.5, 9.7). At week 24, mean serum E2 concentrations were similar in the goserelin 10.8 mg and goserelin 3.6 mg groups (20.3 pg/mL and 24.8 pg/mL, respectively).ConclusionA regimen of 3-monthly goserelin 10.8 mg demonstrated non-inferiority compared with monthly goserelin 3.6 mg for PFS rate at 24 weeks, with similar pharmacodynamic and safety profiles, in pre-menopausal women with ER-positive breast cancer.