CARE Breast Cancer Faculty Canadian Perspectives from ASCO 2013
Abstract 5: aTTom: Long-Term Effects of Continuing Adjuvant Tamoxifen to 10 Years Versus Stopping at 5 Years in 6,953 Women With Early Breast Cancer. R.G. Gray, D. Rea, K. Handley, et al.
Background: Five years of adjuvant tamoxifen in estrogen-receptor-positive (ER+) early breast cancer (EBC), reduces breast cancer recurrence and death rates. Due to preliminary studies, uncertainties remained however as to whether extended tamoxifen duration beyond five years would provide additional benefit. ATLAS2 was the first large, international, randomized trial presented at SABCS 2012, which demonstrated the additional benefit of extended duration tamoxifen from five to ten years. A similarly designed UK-LED study aTTom2 was the subject of much anticipation and was presented at the plenary session at ASCO 2013.
Methods: During 1991–2005, 6,953 women with ER+ (n = 2,755), or ER untested (4,198, estimated 80% ER+ if status known) invasive EBC from 176 UK centers were randomized after five years of tamoxifen, to stop tamoxifen or to continue on to ten years.
Results: Allocation to continued tamoxifen use to ten years reduced breast cancer recurrence overall and was reported to be time dependent and only significant after year six. Longer duration treatment also reduced breast cancer specific mortality and again time dependent, with significance noted only after year nine. Similar benefits were seen with overall mortality and no major increase was seen in non-breast cancer mortality. As expected, increased rates of endometrial cancers were observed in the ten-year duration group.