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.