First-line vs second-line fulvestrant for hormone receptor-positive advanced breast cancer: A post-hoc analysis of the CONFIRM study.

Objectives: The double-blind, phase III CONFIRM study (NCT00099437) evaluated fulvestrant 500 mg vs fulvestrant 250 mg in postmenopausal women with hormone receptor-positive locally advanced/metastatic breast cancer (LA/MBC). This post-hoc analysis investigated the efficacy and safety of fulvestrant given either first-line or second-line for advanced disease.

Materials & Methods: Progression-free survival (PFS) and overall survival (OS) with fulvestrant 500 mg vs fulvestrant 250 mg was evaluated using unadjusted log-rank tests in patients treated in the first- (progression during or within 12 months after completing adjuvant endocrine therapy; n = 387) and second-line (following endocrine therapy for LA/MBC; n = 343) settings.

Results: First-line fulvestrant 500 mg significantly prolonged PFS vs fulvestrant 250 mg (median PFS 5.6 vs 4.2 months; hazard ratio [HR] 0.80; 95% confidence interval [CI] 0.64-1.00; p = .047). Median PFS was numerically greater with second-line fulvestrant 500 mg vs fulvestrant 250 mg (7.9 vs 6.3 months; HR 0.80; 95% CI 0.64-1.02; p = .068). At data cut-off (75.5% maturity), median OS with first-line fulvestrant 500 mg was 23.2 vs 22.1 months with fulvestrant 250 mg (HR 0.87; 95% CI 0.70-1.10; p = .251), and 29.2 vs 22.8 months, respectively, in the second-line (HR 0.75; 95% CI 0.58-0.96; p = .020). The safety profile was broadly comparable between dose groups and across treatment lines, and consistent with the overall patient population.

Conclusion: The superiority of fulvestrant 500 mg over fulvestrant 250 mg in patients with LA/MBC in CONFIRM was consistent in both the first- and second-line settings for PFS, and numerically greater in both settings for OS.