Fulvestrant As Maintenance Therapy after First-Line Chemotherapy in Patients with Hormone Receptor Positive, HER2-negative Advanced Breast Cancer (FANCY), a Prospective, Multicenter, Single Arm Phase 2 Study.

1066 Background: Fulvestrant is potent for treatment of hormone receptor (HR)-positive advanced breast cancer (ABC); however, few data exist for this regimen as maintenance endocrine treatment after chemotherapy (CT). In our phase 2 trial, we aimed to assess efficacy and tolerability of fulvestrant 500mg as maintenance therapy in patients with disease control after first-line CT. Methods: Simon’s two-stage design was used. We enrolled postmenopausal women with histologically confirmed HR-positive, HER2-negative ABC, who achieved disease control after four to eight cycles of first-line CT. Fulvestrant 500 mg was intramuscularly injected on day 1, 15, 29, then every 28 (±3) days subsequently, until disease progression or unacceptable toxicity. The primary endpoint was clinical benefit rate (CBR), secondary endpoint included progression-free survival (PFS) since maintenance treatment, PFS since first-line CT, objective response rate (ORR) and safety. Results: Between Dec 10, 2013, and Sept 30, 2015, 58 patients were enrolled. 25 (43%) patients were deemed as resistance to endocrine treatment, 36 (62%) patients had a visceral disease. Median follow-up was 21 months. After fulvestrant maintenance treatment, 36 patients remained disease stabilising for at least six months, and eight (14%, 95% CI 6-25) patients achieved a response, resulted in a CBR of 76% (95% CI 63-86), which met its primary endpoint. The median PFS since fulvestrant treatment was 16·1 months (95% CI 10·3 to not reached), and median PFS since first-line CT was 19·5 months (95% CI, 15·6 to not reached). 39 (67%) of 58 patients reported at least one adverse event (AE), of which predominantly were grade 1 or 2. The most common grade 3 AEs were increased alanine aminotransferase in two (3%) patients, increased aspartate aminotransferase in one (2%) patient, and arthralgia in one (2%) patient. No patient discontinued treatment due to AE. Conclusions: Fulvestrant 500mg is active in maintenance therapy in non-progrssion patients with HR-positive ABC after first-line CT. Further study is needed to assess long-term outcome of maintenance therapy. Clinical trial information: NCT02000193.