Fulvestrant as Effective as Anastrozole in Breast Cancer

Laurie Barclay, MD

August 16, 2002

Aug. 19, 2002 — In two randomized trials described in the Aug. 15 issue of the Journal of Clinical Oncology, fulvestrant (Faslodex) was as effective as anastrozole for the treatment of women with estrogen receptor (ER)-positive breast cancer who were refractory to tamoxifen.

"Fulvestrant represents an additional treatment option for postmenopausal women with advanced breast cancer whose disease progresses on tamoxifen therapy," write C. K. Osborne, MD, from Baylor College of Medicine in Houston, and colleagues. "Fulvestrant was at least as effective as anastrozole, with efficacy end points slightly favoring fulvestrant."

In this U.S.-based, double-blind, double-dummy, parallel-group study, 400 postmenopausal patients were randomized to receive either fulvestrant, 250 mg by intramuscular injection once monthly, or anastrozole, 1 mg daily by mouth. Median follow-up period was 16.8 months.

Fulvestrant was as effective as anastrozole in terms of time to progression (TTP) (hazard ratio, 0.92; 95% confidence interval [CI], 0.74-1.14; P=.43). Median TTP was 5.4 months with fulvestrant and 3.4 months with anastrozole. Objective response rates were 17.5% in both groups. Clinical benefit rates, defined as the percentage of patients who had complete or partial response or stable disease for at least 24 weeks, were 42.2% for fulvestrant and 36.1% for anastrozole (95% CI, -4.00% to 16.41%; P=.26).

In patients who responded, median duration of response (DOR) from randomization to progression was 19.0 months for fulvestrant and 10.8 months for anastrozole. Among all patients, DOR was significantly greater for fulvestrant than for anastrozole; the ratio of average response durations was 1.35 (95% CI, 1.10-1.67; P<.01). Both treatments were well tolerated.

In the second study, an open, parallel-group, multicenter trial, A. Howell, MD, from Christie Hospital National Health Service Trust in Manchester, U.K., and colleagues randomized 451 women with advanced breast cancer to treatment with fulvestrant or anastrozole. Median follow-up was 14.4 months. Median TTP was 5.5 months for fulvestrant and 5.1 months for anastrozole (hazard ratio, 0.98; CI, 0.80-1.21; P=.84). For fulvestrant compared with anastrozole, objective response rates were 20.7% vs. 15.7% (odds ratio, 1.38; CI, 0.84-2.29; P=.20); clinical benefit rates were 44.6% vs. 45.0%; and median DOR was 14.3 months vs. 14.0 months. Both treatments were generally well tolerated, although 3.2% of fulvestrant-treated patients and 1.3% of anastrozole-treated patients withdrew from treatment because of an adverse event.

"These data confirm that fulvestrant is an additional, effective, and well-tolerated treatment for advanced breast cancer in postmenopausal women whose disease progressed on prior endocrine therapy," the authors write.

In an accompanying editorial, I. Craig Henderson, from the University of California at San Francisco, speculates that fulvestrant and anastrozole together might be even more effective than single-agent therapy. Fulvestrant is a pure estrogen antagonist, unlike tamoxifen, which has partial agonist effects, and the aromatase inhibitors, which reduce the estrogen available to the cancer cell.

"It is possible that combinations of fulvestrant and aromatase inhibitors will be effective," he writes. "While these new therapies may be confusing to clinicians and patients at this time, they also offer promise of much more effective, nontoxic treatment that will both palliate symptoms and prolong the lives of patients with breast cancer."

The U.S. Food and Drug Administration recently approved Faslodex (fulvestrant) for the treatment of advanced breast cancer. AstraZeneca funded these studies.

J Clin Oncol. 2002;20(16): 3365-3368, 3386-3395, 3396-3403

Reviewed by Gary D. VVVogin, MD

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