Anti-estrogen Combo Extends Life for Older Women with Metastatic Breast Cancer
Anastrozole with fulvestrant better than single drug for hormone-sensitive breast cancer
Dec. 9, 2011 - Post-menopausal women with hormone receptor-positive metastatic breast cancer may have a new treatment
option that could lengthen their lives by months, according to results of a study by the SWOG clinical trials network that were presented this
week at the 2011 CTRC-AACR San Antonio Breast Cancer Symposium.
The combination of the two anti-estrogen drugs anastrozole and fulvestrant used in the SWOG S0226 trial extended the
median survival time of women with breast cancer by more than six months compared to those who underwent standard treatment with anastrozole
alone (47.7 months vs 41.3 months).
The combination therapy also lengthened the median time to disease progression (15 months vs 13.5 months).
Lead study coordinator Rita Mehta, M.D., of the University of California, Irvine Medical Center says the results of the
phase III trial are particularly exciting because "these patients have not had a new treatment that gave them an overall survival benefit in
more than a decade."
Anastrozole (Arimidex) and fulvestrant (Faslodex) are both already used in treating breast cancer, though not in
combination. The former reduces the production of tumor-promoting estrogen, while the latter interferes with the receptors that allow estrogen
to signal cells to grow and reproduce.
Researchers think it's these two different modes of action together that make the combination so effective against
hormone receptor-positive breast cancer, the subtype that accounts for more than half of all breast cancers.
"If we take away estrogen and the estrogen receptor, the two together should be better than just doing one at a time,"
Starting in the spring of 2004, she and colleagues at 72 other institutions enrolled 707 postmenopausal women with
metastatic hormone receptor-positive breast cancer to the trial.
Women were assigned at random to one of the study's two arms. Patients on both arms got a standard 1 mg oral daily dose
of anastrozole. Those on the combination arm also got a 250 mg injection of fulvestrant every 28 days, after an initial set of injections to
raise the level of fulvestrant in their bloodstream. Researchers saw no significant differences in how well patients tolerated the two
The overall survival benefit was particularly strong in women who had not previously had tamoxifen therapy for their
breast cancer. Among this tamoxifen-naive group (about 60 percent of patients in each arm), median overall survival time on the combination
therapy was 47.7 months as compared to 39.7 months for those taking only anastrozole.
The trial researchers are hesitant, however, to focus too much attention on this aspect of the findings. Because plans to
analyze the results by prior tamoxifen use were not built into the original trial design, the results of that analysis must clear a higher bar
to be found statistically significant.
"We need to better understand other possible factors, since the prior tamoxifen factor could be a false lead from an
unplanned analysis," says Mehta, who is eager to see whether even more patients might benefit from this combination treatment.
"The next step for researchers," she says, "would be to try the combination in even earlier stages of breast cancer to
test whether long-term cures could be increased at those stages."
Funding for the trial came primarily from the National Cancer Institute, one of the National Institutes of Health.
Additional support, and the anastrozole and fulvestrant for the trial, were provided by AstraZeneca Pharmaceuticals LP, of Wilmington, Del.
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