Austrian Researchers Demonstrate Benefit in Switch to Anastrozole

Writing in the Lancet (2005; 366: 455-62) Austrian researchers have completed a study which demonstrated the benefit of postmenopausal women with endocrineresponsive early breast cancer switching to anastrozole after 2 years’ adjuvant tamoxifen.

For over twenty years, tamoxifen has been the standard adjuvant treatment for postmenopausal women with hormone responsive early breast cancer. However, compared to tamoxifen, the aromatase inhibitor anastrozole, has shown improved efficacy and tolerability as an initial adjuvant therapy. To determine whether women being treated with adjuvant tamoxifen would benefit from a switch to anastrozole, researchers conducted an analysis on data combined from two prospective, multicentre, randomised, open-label trials. The primary endpoint of this study was event-free survival, where an event was defined as local or distant metastasis, or contralateral breast cancer (analysis was by intention to treat). The inclusion criteria for both trials was that participants were postmenopausal women with hormone-sensitive early breast cancer who had completed 2 years’ adjuvant oral tamoxifen (20 or 30 mg daily). 3,224 patients met this criteria and were included in analyses. The participants were randomised to receive either 1 mg oral anastrozole (n=1618) or 20 or 30 mg tamoxifen (n=1606) daily for the remainder of their adjuvant therapy. Researchers found a 40% decrease in the risk for an event in the anastrozole group as compared with the tamoxifen group (67 events with anastrozole vs 110 with tamoxifen, hazard ratio 0.60, 95% CI 0.44-0.81, p=0.0009) at a median follow-up of 28 months. The study showed both treatments were well tolerated. There were significantly more fractures (p=0.015) and significantly fewer thromboses (p=0.034) in patients treated with anastrozole than in those on tamoxifen. Researchers concluded that their findings support a switch from tamoxifen to anastrozole in patients who have completed 2 years’ adjuvant tamoxifen.