Phase III randomized adjuvant study of tamoxifen alone versus sequential tamoxifen and anastrozole in postmenopausal women with hormone-responsive breast cancer: N-SAS BC03 study.

Abstract

Abstract Abstract #1138 Background. Clinical trials conducted in Western countries have shown that improved disease-free survival (DFS) is associated with the use of aromatase inhibitors instead of tamoxifen in postmenopausal women with early breast cancer. Pharmacogenetic differences in drug metabolizing genes may cause ethnic differences in the response or tolerability to aromatase inhibitors, as well as tamoxifen. In fact, improved DFS by extending the use of letrozole after tamoxifen for 5 years has not been confirmed in women from minority groups (Ann Oncol. 2006 17(11):1637-43). Therefore, assessment of the efficacy of aromatase inhibitors in non-white women is warranted. We report the results of switching adjuvant therapy from tamoxifen to anastrozole in postmenopausal Japanese women with breast cancer enrolled in an open-label, randomized clinical trial (N-SAS BC03 study). Patients and Methods. From November 2002 to December 2005, 706 postmenopausal women with hormone-receptor-positive breast cancer who were receiving adjuvant therapy with tamoxifen for 1 to 4 years were randomly assigned to either continue tamoxifen or to switch to anastrozole; the total duration of treatment was 5 years. Primary endpoints were DFS and adverse events. Secondary endpoints included relapse-free survival (RFS), overall survival (OS) and QOL. Results. After a median follow-up of 42 months (range, 3.2-60), there were 26 events in the anastrozole group as compared with 37 in the tamoxifen group related to DFS, and 15 events in the anastrozole group as compared with 28 in the tamoxifen group related to RFS. The unadjusted hazard ratio was 0.69 (95 percent confidence interval, 0.42 to 1.14; P=0.06 by the log-rank test) for DFS and 0.52 (95 percent confidence interval, 0.28 to 0.98; P=0.02 by the log-rank test) for RFS, both in favor of anastrozole. There was no difference in OS (p=0.49). Conclusion. Switching from tamoxifen to anastrozole was confirmed to be associated with a lower disease recurrence rate than continuing tamoxifen in postmenopausal Japanese women with breast cancer. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 1138.