SWOG: Two Hormonal Agents Extend Survival over Anastrozole Alone in Metastatic Breast Cancer

December 2011, Vol 2, No 7

San Antonio, TX—Two antiestrogen agents may be better than one in the treatment of metastatic hormone receptor-positive breast cancer patients, according to a study conducted by the Southwest Oncology Group (SWOG) clinical trials network and presented at the 2011 CTRC-AACR San Antonio Breast Cancer Symposium.

In SWOG 0226, which involved 72 centers, 707 postmenopausal women with metastatic hormone receptor– positive breast cancer were randomized to standard treatment with 1 mg daily of anastrozole (Arimidex) alone or to the combination of anastrozole plus a 250-mg monthly injection of fulvestrant (Faslodex), after an initial 500-mg injection on day 1 and a 250- mg injection on day 14.

The combination extended median overall survival time by more than 6 months compared with anastrozole alone (47.7 months vs 41.3 months, respectively), representing a 29% risk reduction (P = .049), and increased disease-free survival by about 6 weeks (15 months vs 13.5 months, respectively), reported study investigator Rita S. Mehta, MD, clinical oncologist, at the University of California, Irvine Medical Center.

“These patients have not had a new treatment that gave them an overall survival benefit in more than a decade,” Dr Mehta said.

Anastrozole reduces the production of tumor-promoting estrogen, and fulvestrant interferes with the receptors that allow estrogen to signal cells to grow and reproduce. The complementary modes of action of these 2 agents—“taking away estrogen and the estrogen receptor as well”—appears to enhance the efficacy of endocrine therapy in this subset of patients, which comprises more than 50% of all cases of breast cancer.

The benefit of the combination therapy was most pronounced among women who had not received tamoxifen (Nolvadex), whose median survival with the combination was 47.7 months, versus 39.7 months with anastrozole alone—a 26% risk reduction (P = .036); patients who had previously received tamoxifen had only a nonsignificant 9% reduction in risk.

Although this finding may suggest that the real benefit is only for patients who are tamoxifen-naïve, it “could also be a false lead from an unplanned analysis,” Dr Mehta said. —CH

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