ATLAS 10 v 5 years of adjuvant tamoxifen (TAM) in ER+ disease effects on outcome in the first and in the second decade after diagnosis

SUMMARY: Historically, adjuvant treatment with tamoxifen beyond five years has not been recommended, as the benefit of tamoxifen beyond five years was unknown but there was an increased risk of endometrial cancer. (Tamoxifen Treatment for Breast Cancer and Risk of Endometrial Cancer: A Case-Control Study, J Natl Cancer Inst 2005; 97: 375-384). The ATLAS trial has now shed some light on the duration of tamoxifen treatment. In this study, 6846 women with ER positive breast cancer were enrolled between 1996 and 2005 and following five years of adjuvant tamoxifen were randomized to five additional years of tamoxifen or observation. Women who continued on tamoxifen had a 25% lower recurrence rate and 29% lower breast cancer mortality rate compared with women who stopped tamoxifen after five years. This significant benefit was seen in the second decade after diagnosis with little benefit seen in the 5-9 year period after diagnosis. There was a higher cumulative risk of death from endometrial cancer for those who continued tamoxifen beyond 5 years compared to those who did not (0.4% vs 0.2%). It appears that the reduction in breast cancer deaths outweigh the risk of endometrial cancer and other adverse events associated with longer duration of tamoxifen use. This new information will help physicians make appropriate treatment recommendations for those patients on adjuvant tamoxifen. Davis C, Hongchao P, Godwin J, et al. CTRC-AACR San Antonio Breast Cancer Symposium, 2012; Abstract S1-2.