Study: Fulvestrant More Effective for Some With Advanced Breast Cancer

Fulvestrant is more effective than anastrozole in the treatment of postmenopausal women with advanced breast cancer whose disease worsened with prior anti-estrogen treatment, according to a study published in the Journal of Clinical Oncology.

In some cases, hormones naturally occurring in the body can fuel cancer cells. Endocrine (anti-estrogen) therapy, such as tamoxifen, adds to or interferes with those hormones to block their effects on cancer cells.

Fulvestrant is a new anti-estrogen therapy from a class of agents known as selective estrogen receptor downregulators. Researchers believe fulvestrant may offer a longer duration of response with a decreased risk of thromboembolism and endometrial side effects that have been linked with tamoxifen in some patients.

Anastrozole is an aromatase inhibitor and works by blocking the conversion of aromatizable steroids to estrogen. This is in contrast to the mechanism of action of anti-estrogens such as tamoxifen, which block estrogen receptors in some tissues, and activate estrogen receptors in others.

U.S. and British researchers compared the effectiveness and tolerability of fulvestrant with anastrozole in the treatment of advanced breast cancer in patients whose cancer worsened with previous anti-estrogen therapy.

A total of 400 postmenopausal women were given either an injection of fulvestrant (250 mg) once each month or a daily oral dose of anastrozole (1 mg). The primary measurement used in the study was the time to disease progression and secondary measurements were response rate, duration of response and tolerability. The patients were followed for 16.8 months.

Researchers found that fulvestrant was as effective as anastrozole in time to disease progression. Clinical benefit rates (complete response, partial response, stable disease) were 42.2 percent for fulvestrant and 36.1 percent for anastrozole. In the patients who responded to the drug, the average duration of response was 19.0 months for fulvestrant and 10.8 months for anastrozole. Using all patients, duration of response was significantly greater for fulvestrant compared with anastrozole. Both treatments were well tolerated.

"Fulvestrant was at least as effective as anastrozole, with efficacy end points slightly favoring fulvestrant," concluded the researchers. "Fulvestrant represents an additional treatment option for postmenopausal women with advanced breast cancer whose disease progresses on tamoxifen therapy.

Other sources: Journal of Clinical Oncology