Tamoxifen therapy for five years after surgery is the established treatment for postmenopausal women with hormone-sensitive breast cancer. However, its use is associated with several side-effects including endometrial cancer and blood-clotting disorders. The ATAC investigators led by Michael Baum from University College London, UK, and colleagues was an international study which aimed to compare the safety and efficacy of tamoxifen with anastrozole alone and the combination of both drugs for 5 years.
9366 postmenopausal women from 21 countries who had undergone breast-cancer surgery were studied; 3125 were randomly assigned anastrozole, 3116 tamoxifen, and 3125 combination therapy. The average follow-up was just under three years (33 months).
Three-year disease-free survival was 2% greater among women given anastrozole (89.4%) compared with those given tamoxifen (87.4%). Combination therapy with both drugs showed no additional benefit compared with women given tamoxifen. Anastrozole was better tolerated than tamoxifen with respect to endometrial cancer, vaginal bleeding and discharge, stroke, venous thromboembolic events, and hot flushes. Tamoxifen was significantly better tolerated than anastrozole with respect to musculoskeletal disorders and bone fractures.
Michael Baum comments: "Evidence from this first analysis of the ATAC trial is encouraging. An important consideration at this time is how to treat newly diagnosed patients. An overall assessment of the benefits versus harm, based on current data, supports the use of anastrozole for the adjuvant treatment of early breast cancer in postmenopausal women, meaning that there is now a choice of adjuvant endocrine therapy for postmenopausal women with hormone-responsive tumours."
Contact: Mrs Joan Houghton, CRUK and UCL Clinical Trials Centre, Royal Free & University College Medical School, Stephenson House, 158-160 Gower Street, LONDON NW1 2ND, UK; T) +44 (0)20 7679 8040; F) +44 (0)20 7679 8001; E) j.houghton@ctc.ucl.ac.uk
The Lancet