Switching to anastrozole after two years of tamoxifen may improve outcomes in early breast cancer, researchers have found.
The ARNO 95 trial compared switching to anastrozole after two years of tamoxifen treatment to the continuation of tamoxifen for five years in postmenopausal women with oestrogen receptor positive early breast cancer. The results have been published early online in the Journal of Clinical Oncology.
The authors note that the results of this study have been presented in a combined analysis and in a meta-analysis, but that this is the first report of the ARNO 95 study results alone. This open-label trial randomised postmenopausal women who had undergone primary surgery for early breast cancer and had received two years of continuous tamoxifen therapy (20mg or 30mg daily) to treatment with anastrozole (1mg/day; n=489) or to continue with tamoxifen (20mg or 30mg daily; n=490) for an additional three years.
The primary endpoint of the study was disease-free survival (DFS; including local or distant recurrence, new contralateral breast cancer, or death); secondary endpoints included overall survival (OS) and toxicity.
The main results were:
• Switching to anastrozole resulted in an improvement in DFS compared to continuing with tamoxifen (hazard ratio 0.66; 95% CI, 0.44–1.00; p=0.049). Estimated three-year DFS rates were 93.5% for anastrozole and 89.3% for tamoxifen.
• Switching to anastrozole was associated with improved overall survival compared with continuing on tamoxifen (HR, 0.53; 95% CI, 0.28–0.99; p=0.045)
• Fewer patients who switched to anastrozole reported serious adverse events (22.7% vs 30.8%) compared with those who continued on tamoxifen, mainly due to there being more patients in the tamoxifen group with endometrial events (OR 0.66; 95% CI, 0.49–0.89; p=0.0065).
The authors conclude: “The results show that patients switched to anastrozole after an initial period of tamoxifen therapy experience significant improvements in terms of disease-free and overall survival. Our results provide additional evidence that five years of tamoxifen is no longer the optimum adjuvant therapy for postmenopausal women with hormone receptor positive early breast cancer, and will be of considerable relevance to the large number of women currently receiving long-term endocrine therapy with tamoxifen.”
J Clin Oncol, published early online 11/6/2007