FDA drug approval summaries: fulvestrant

Area of Science:

• Endocrinology
• Medical Oncology
• Pharmacology

Background:

• Hormone-sensitive breast cancer patients progressing on tamoxifen may benefit from second-line endocrine therapy.
• Fulvestrant is a selective estrogen receptor antagonist designed for intramuscular administration.
• Estrogen receptor-positive metastatic breast cancer requires effective post-tamoxifen treatment strategies.

Purpose of the Study:

• To compare the efficacy and safety of fulvestrant with anastrozole in postmenopausal women with advanced breast cancer.
• To evaluate fulvestrant as a second-line endocrine therapy after progression on tamoxifen.

Main Methods:

• Two Phase III studies (North American and European) enrolled 851 postmenopausal women with advanced breast cancer.
• Patients received either fulvestrant (250 mg monthly IM injection) or anastrozole (1 mg daily).
• Hormone sensitivity was determined by receptor status or prior response to endocrine therapy; over 96% had prior tamoxifen exposure.

Main Results:

• Response rates were comparable between fulvestrant (17-20%) and anastrozole (15-17%) across both studies.
• No statistically significant differences were observed in time to progression or survival between the treatment arms.
• Common adverse events included injection-site reactions and hot flashes; joint disorders were more frequent with anastrozole.

Conclusions:

• Fulvestrant demonstrated comparable efficacy to anastrozole in advanced hormone-sensitive breast cancer patients progressing after tamoxifen.
• Fulvestrant 250 mg monthly IM injection is an approved treatment option for this patient population.
• The safety profile of fulvestrant is acceptable, with distinct adverse event patterns compared to anastrozole.