The ATAC trial: the vanguard trial for use of aromatase inhibitors in early breast cancer.

The Anastrozole, Tamoxifen, Alone or in Combination (ATAC) trial was the first trial to explore the use of aromatase inhibitors in post-menopausal women with early breast cancer and is the largest published cancer treatment trial in breast cancer. The main results have been published at 33-, 47- and 68-month median follow-up, and further analyses are planned for the end of 2007 and in 2010. This trial demonstrated that 5 years of treatment with anastrozole was generally better tolerated than 5 years of treatment with tamoxifen, and led to lower recurrence rates, especially in receptor-positive women (26% reduction). The side-effect profile was different than that for tamoxifen, with fewer hot flushes, gynecologic symptoms, endometrial cancers, strokes and thromboembolic events; however, an increased incidence of fractures, joint symptoms and carpal tunnel syndrome was observed. Future analyses will determine whether benefits and fracture rates persist after stopping treatment, and the extent to which currently marginal benefits on late end points, such as distant recurrence and death after recurrence, are sustained or improved.