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Fulvestrant--a novel estrogen receptor antagonist for the treatment of advanced breast cancer.

Endocrine therapy is often the preferred treatment option for postmenopausal women with hormone receptor-positive breast cancer. However, as many patients eventually develop resistance there is a need for novel, efficacious and well-tolerated treatments that lack cross-resistance with current therapies. This review describes the development of fulvestrant (Faslodex), an estrogen receptor antagonist with a different and distinct mode of action and no agonist effects. Phase III clinical trials in postmenopausal women with advanced breast cancer have found fulvestrant at the approved dose of 250 mg/month to be at least as effective and well tolerated as anastrozole following disease progression or recurrence on tamoxifen, and as effective as exemestane following disease progression or recurrence on nonsteroidal aromatase inhibitors. In addition, fulvestrant has also demonstrated activity in patients with visceral and HER2+ disease, who are generally regarded as being less responsive to endocrine therapy. Data from a recent neoadjuvant study suggest that a higher dose of fulvestrant may possess greater activity. Trials evaluating higher fulvestrant doses, and regimens combining fulvestrant with aromatase inhibitors or agents targeting growth factor receptors, are ongoing and will help determine the optimum use of fulvestrant in the endocrine treatment sequence for postmenopausal women with advanced breast cancer.