The combination of anastrozole (Arimidex®) and fulvestrant (Faslodex®) prolonged overall survival and progression-free survival in postmenopausal women with previously untreated hormone receptor-positive metastatic breast cancer compared to Arimidex alone, according to the results of a study published in the New England Journal of Medicine.
Each year roughly 200,000 U.S. women are diagnosed with breast cancer. Many of these breast cancers are hormone receptor-positive, meaning that they are stimulated to grow by the circulating female hormones estrogen and/or progesterone. Treatment of hormone receptor-positive breast cancer often involves hormonal therapies that suppress or block the action of estrogen.
Arimidex is a type of hormone therapy known as an aromatase inhibitor and works by suppressing the production of estrogen in postmenopausal women. Faslodex is a type of hormonal therapy known as an estrogen receptor antagonist and works by binding to estrogen receptors and degrading them. Both drugs are approved for the treatment of postmenopausal women with metastatic breast cancer.
To evaluate the drugs in combination, researchers conducted a trial involving 694 women who were randomly assigned to receive Arimidex alone or Arimidex and Faslodex combined. All women in the study had cancer that was hormone-receptor positive and none of them had been previously treated with chemotherapy, immunotherapy, or hormone therapy to stop the spread of disease.
The results indicated that the combination was superior to the single agent therapy. The median progression-free survival was 15 months in the combination group, compared to 13.5 months in the Arimidex alone group. Overall survival was also longer in the combination group—47.7 months compared to 41.3 months in the single agent group. Of note, not all patients assigned to anastrozole subsequently received fulvestrant. Furthermore, another study looking at the combination of anastrozole and fulvestrant failed to show superiority over anastrozole alone.
Both groups had mild to moderate side effects such as joint pain and hot flashes. Although the rate was higher in the combination group, it was not statistically significant.
The researchers concluded that the combination of Arimidex and Faslodex was superior to Arimidex alone for the treatment of hormone-receptor positive metastatic breast cancer—even though the dose of Faslodex was below the current standard dose. However, the results of this study have to be reconciled with the less favorable results from the other study that evaluated this combination. Many oncologists continue to believe that the optimal hormonal therapy approach for women newly diagnosed with metastatic breast cancer remains uncertain.
Mehta RS, Barlow WE, Albain KS, et al. Combination anastrozole and fulvestrant in metastatic breast cancer. New England Journal of Medicine. 2012; 367:435-444.
Posted August 6, 2012