123P Goserelin 10.8 mg and 3.6 mg depots in breast cancer (BC): A large real-world noninferiority study

BC pts in China (median age 48-50 y), with est. 60% being premenopausal, are younger than those in western countries. As an effective ovarian function suppression therapy that improves survival for premenopausal hormone receptor-positive (HR+) BC pts, the 3-monthly goserelin 10.8 mg depot offers more convenience with reduced visits and clinician burden compared with the monthly 3.6 mg depot. We conducted the largest real-world study (RWS) to date in China with 8 years of data to validate the noninferiority of goserelin 10.8 mg to the 3.6 mg depot. This multicenter, retrospective-prospective, noninferiority study used medical record data to compare goserelin 10.8 mg with 3.6 mg in suppressing estradiol (E2) levels in premenopausal HR+ BC pts. Propensity score matching (PSM) ensured baseline comparability. The primary endpoint was the proportion of pts with E2 suppression to postmenopausal level at Wk 12±4. Difference in proportions and 95% CI was calculated by Newcombe-Wilson score method. The noninferiority margin was -10%. Subgroup and sensitivity analyses assessed confounder effects and result robustness. From 1 Jan 2015 to 15 Dec 2023, 15,629 pts from 16 hospitals nationwide were screened, with 1,060 eligible pts included in the full analysis set (10.8 mg group: 382; 3.6 mg group: 678). Post PSM, the primary endpoint was analyzed in 590 pts (295 in each group). At Wk 12±4, the proportion of pts with E2 suppression was 99.1% (95% CI: 96.9%, 99.8%) for goserelin 10.8 mg and 95.3% (95% CI: 91.0%, 97.6%) for goserelin 3.6 mg. The difference was 3.8% (95% CI: 0.6%, 8.1%) with the lower limit of 95% CI greater than the noninferiority margin. All subgroup analyses, including those based on age (≤45/>45 y) and previous chemotherapy (yes/no), and all sensitivity analyses on the primary endpoint were consistent with the main analysis (Table).Table: 123PSensitivity analyses on the primary endpointAnalysis†Timepoint, WkProportion of Pts with E2 Suppression, % (n/N)Difference in Proportions, % (95% CI)P value10.8 mg3.6 mgEndpoint redefined as the proportion of pts with E2 suppression in all measurements between Wk 4 and 164–1699.2 (259/261)94.4 (185/196)4.8 (1.7, 9.0)0.002Excluded pts who switched between goserelin 10.8 mg and 3.6 mg dosages12±499.1 (223/225)94.7 (144/152)4.4 (0.9, 9.2)0.017For the goserelin 3.6 mg group, only pts who received ≥2 doses were included∗99.1 (217/219)95.8 (159/166)3.3 (0.1, 7.6)0.043†Three key analyses out of 11 conducted are shown. *Rematched with 279 included in each group. Open table in a new tab †Three key analyses out of 11 conducted are shown. *Rematched with 279 included in each group. This large RWS with rigorous design validated the noninferiority of goserelin 10.8 mg 3-monthly to 3.6 mg monthly in Chinese pts with HR+ BC.