Coadministration of anastrozole (Arimidex) and fulvestrant (Faslodex) prolonged survival more effectively than did anastrozole alone or sequential therapy with the two agents among women with hormone-receptor (HR)-positive metastatic breast cancer.  

In the study leading to this finding, 707 postmenopausal women with previously untreated metastatic breast cancer were randomized to one of two groups. Members of group 1 received oral anastrozole 1 mg/day, with crossover to fulvestrant injection alone (500 mg on day 1 and 250 mg on days 14 and 28 and monthly thereafter) strongly encouraged if the disease progressed. The group 2 participants were given anastrozole and fulvestrant in combination. Anastrozole is an aromatase inhibitor; fulvestrant binds to estrogen receptors.

Median progression-free survival was 13.5 months in group 1, compared with 15 months in group 2. The combination-therapy patients also had longer overall survival (median 47.7 months, compared with 41.3 months), despite the fact that 41% of the women in group 1 crossed over to fulvestrant after disease progression. The rates of grades 3-5 toxic effects did not differ significantly between the two sets of patients, but three deaths that were possibly associated with treatment occurred in the combination-therapy group (N Engl J Med. 2012;367:435-444).

The coadministration of anastrozole and fulvestrant was superior to anastrozole therapy alone or anastrozole followed by fulvestrant, even with the fulvestrant dose being lower than the current standard.