Emerging data on the efficacy and safety of fulvestrant, a unique antiestrogen therapy for advanced breast cancer.

INTRODUCTION: Fulvestrant is an antiestrogen therapy with a unique mechanism of action. Unlike the selective estrogen receptor modulator tamoxifen, fulvestrant has no known estrogen agonist activity and is considered a pure antiestrogen. Its primary mechanism of action is thought to result from downregulation of the estrogen receptor (ER). Considerable data have demonstrated the efficacy of fulvestrant in postmenopausal women with ER-positive advanced breast cancer, both in the first-line setting and following disease progression on tamoxifen or aromatase inhibitors. Recent studies report improved benefit with alternative dosing strategies. At all administration schedules, fulvestrant has an excellent safety profile with no significant adverse effects. AREAS COVERED: This article provides a review of the mechanism of action of fulvestrant and the preclinical and clinical data evaluating its use as a form of endocrine therapy. The reader will gain insight into the pharmacologic properties of the drug and its role in the treatment of advanced hormone receptor-positive breast cancer in postmenopausal women. EXPERT OPINION: Based on data demonstrating the efficacy of fulvestrant, including prolonged clinical benefit in many patients, this well-tolerated antiestrogen is an important therapy for breast cancer. The optimal position of fulvestrant in the sequence of endocrine therapies for postmenopausal women and its role in combination regimens are not yet resolved.