The ‘Arimidex’, Tamoxifen, Alone or in Combination (ATAC) Trial: A Step Forward in the Treatment of Early Breast Cancer

The ATAC trial is the first study to compare a third-generation aromatase inhibitor (AI), anastrozole, with tamoxifen for the adjuvant treatment of early breast cancer. Analyses at 33 and 47 months of median follow-up showed that anastrozole significantly prolonged disease-free survival (DFS) and time to recurrence (TTR), and reduced the incidence of contralateral breast cancer, compared with tamoxifen. Results of the Completed Treatment Analysis at 68 months of median follow-up confirmed the superiority of anastrozole over tamoxifen. The absolute difference in DFS between anastrozole and tamoxifen continued to increase beyond completion of treatment and early improvements in DFS and TTR have translated into a benefit in time to distant recurrence. Benefits of anastrozole over tamoxifen were maintained without a detrimental impact on quality of life. Mature safety data with extensive patient exposure indicate that overall, anastrozole has a favourable safety profile compared with tamoxifen. Importantly, a decrease in the odds ratio of cardiovascular events was observed with anastrozole compared with tamoxifen. The ATAC trial provides the most mature data of any AI trial and has enabled the evaluation of a full risk:benefit profile of anastrozole.