A Phase II Study of Fulvestrant 500 mg as Maintenance Therapy in Hormone Receptor-Positive, Human Epidermal Growth Factor Receptor 2-Negative Patients with Advanced Breast Cancer After First-Line Chemotherapy

Lessons Learned Fulvestrant 500 mg maintenance therapy showed a clinical benefit rate of 76% and median progression-free survival of 16.1 months in patients who achieved objective responses or disease control after first-line chemotherapy. Adverse events with fulvestrant maintenance therapy were consistent with the known safety profile of the drug. Background Evidence for maintenance hormonal therapy after chemotherapy for estrogen receptor (ER)-positive/human epidermal growth factor receptor 2 (HER2)-negative advanced breast cancer is scarce. This study aimed to evaluate the efficacy of fulvestrant 500 mg maintenance therapy in patients after first-line chemotherapy. Methods We enrolled postmenopausal women with ER-positive/HER2-negative advanced breast cancer who attained tumor responses or disease control with four to eight cycles of chemotherapy as first-line treatment. Fulvestrant 500 mg was injected on days 1, 15, and 29 and every 28 (+/- 3) days thereafter. The primary endpoint was the clinical benefit rate (CBR); the secondary endpoints included the objective response rate (ORR), progression-free survival (PFS), and safety. Results We included 58 patients; the median follow-up duration was 32.6 months. The CBR since commencing fulvestrant maintenance therapy was 76% (95% confidence interval [CI], 63%-86%), and ORR was 14% (95% CI, 6%-25%); eight patients achieved partial response. The median PFS for fulvestrant maintenance therapy was 16.1 months (95% CI, 10.3-21.0 months). Thirty-nine patients (67%) reported at least one adverse event, of which most were grade 1/2, whereas three patients (5%) reported grade 3 adverse events. Conclusion Fulvestrant 500 mg is a feasible and promising hormonal maintenance strategy in patients with ER-positive/HER2-negative advanced breast cancer who have no disease progression after first-line chemotherapy.