ATAC results confirm superiority of anastrozole vs. tamoxifen for early breast cancer

Cuzick J. Lancet Oncol. 2010;doi:10.1016/S1470-2045(10)70257-6.

The 10-year follow-up results of the ATAC trial have confirmed the superior efficacy and safety of the aromatase inhibitor anastrozole compared with tamoxifen for the treatment of postmenopausal women with hormone-sensitive early breast cancer.

Although the efficacy of aromatase inhibitors, such as anastrozole, vs. tamoxifen in the adjuvant setting has been confirmed in several trials since the initial results of the ATAC trial, this long-term data provides “important long-term evidence supporting the previous findings,” according to the researchers.

“These trials have led to changes in all major guidelines for breast cancer treatment to now recommend the use of an aromatase inhibitor in the adjuvant treatment of early ER-positive breast cancer,” the researchers wrote.

“The present study suggests that, at least for anastrozole, the benefits of anastrozole are maintained or extended with long-term follow-up and provides more support for the use of anastrozole as the initial adjuvant treatment in this setting.”

In the study, women with early breast cancer were randomly assigned anastrozole plus a tamoxifen placebo, or tamoxifen plus an anastrozole placebo. In both the whole patient population and just hormone-receptor positive patients, outcomes for the primary endpoint of DFS, and the secondary endpoints of time to recurrence, time to distant recurrence, incidence of new contralateral breast cancer, OS and death with or without recurrence were calculated.

At a median follow-up of 120 months, the full study population still showed significant improvements when assigned anastrozole for DFS (HR=0.91; 95% CI, 0.83-0.99), time to recurrence (HR=0.84; 95% CI, 0.75-0.93), and time to distant recurrence (HR=0.87; 95% CI, 0.77-0.99).

Results were also in favor of anastrozole in just those patients with hormone-receptor positive disease. In these patients anastrozole had superior DFS (HR=0.86; 95% CI, 0.78-0.95), time to recurrence (HR=0.79; 95% CI, 0.70-0.89) and time to distant recurrence (HR=0.85; 95% CI, 0.73-0.98). The absolute difference in distant recurrence rates in hormone-receptor positive patients was 2.7% at 10 years for those assigned anastrozole.

Although the researchers found that fewer deaths after recurrence occurred in hormone-receptor positive women assigned anastrozole compared with tamoxifen, there was little difference in overall mortality.

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