P1-08-09 Real-world outcomes comparing 3-monthly with monthly goserelin implant in premenopausal women with breast cancer

Women aged 18-55 years without evidence of postmenopausal status at initial BC diagnosis and exposed to goserelin 3.6 mg or 10.8 mg post-BC diagnosis in the ConcertAI Patient360™ dataset were included in the study. Inverse probability treatment weighting (IPTW) was used to ensure the comparability of baseline demographic and clinical characteristics between the two cohorts. The primary outcome was the real-world disease-free survival (rwDFS) rate at 12 months to assess the non-inferiority of 3-monthly goserelin 10.8 mg vs. monthly goserelin 3.6 mg, and the non-inferiority margin was set at -15% between treatment groups based on published oncology clinical trials. No non-inferiority testing was carried out for other endpoints. Weighted Kapan-Meier analysis was used to characterize rwDFS, overall survival (rwOS), and time to treatment discontinuation (rwTTD) for patients who received 3-monthly goserelin 10.8 mg and monthly goserelin 3.6 mg.

A total of 575 patients received goserelin 3.6 mg and 123 received goserelin 10.8 mg. Post-IPTW, the 3.6 mg cohort had a median age of 41 years, 70.3% white; 68.3% infiltrating ductal carcinoma histology, 41.7% ECOG 0-1, and 61.0% early stage BC at treatment, and the 10.8 mg cohort had a median age of 42 years, 69.9% White, 70.2% infiltrating ductal carcinoma histology, 36.4% ECOG 0-1, and 61.0% early stage BC at treatment. The 12-month rwDFS rates were 76.6% for the 3.6 mg cohort and 79.2% in the 10.8 mg cohort, with a treatment difference of 2.65% (95% CI: -1.75%, -7.04%), supporting the non-inferiority of goserelin 10.8 mg to 3.6 mg at the -15% margin. The rwTTD rates, reported as the proportion of patients on goserelin treatment at 12 months and 24 months for goserelin 3.6 mg vs.10.8 mg, were 39.6 % vs. 51.2% and 23.1% vs. 32.4%, respectively. The median rwDFS and median rwOS were not reached at the 60-month follow-up. The rwDFS rates at 3-years and 5-years for goserelin 3.6 mg vs. 10.8 mg were 61.5% vs. 63.4% and 55.8% vs. 46.9%, respectively. The rwOS rates at 1-year, 3-years, and 5-years for goserelin 3.6 mg vs. 10.8 mg were 92.9% vs. 97.4%, 81.3% vs. 86.2%, and 69.0% vs. 67.4%, respectively.

This real-world analysis indicates that 3-monthly goserelin 10.8 mg is non-inferior to monthly 3.6 mg among premenopausal BC women in terms of 12-month rwDFS rate. This finding may support the use of the goserelin 10.8 mg 3-monthly implant as an alternative treatment option for this patient population.