Management of early breast cancer involves aromatase inhibitors (AIs) and tamoxifen to prevent recurrence during and after treatment. To investigate their relative efficacy, the Early Breast Cancer Trialists’ Collaborative Group undertook a meta-analysis of 31,920 postmenopausal women with oestrogen-receptor-positive early breast cancer in nine randomised clinical trials.
Results showed that taking an AI for five years reduced ten-year breast cancer mortality by around 15% compared with taking tamoxifen for five years (two-sided P=0.009). This was equivalent to around a 40% reduction versus no treatment. In the first four years of treatment, AIs also reduced recurrence rates by around 30% compared with tamoxifen (two-sided P<0.0001). The relative risks differed little by age, body mass index, stage, grade, progesterone receptor status or HER2 status.
In light of these findings, the authors of The Lancet study (online, 23 July 2015
propose a review of gui
delines that recommend beginning treatment with tamoxifen.
 Early Breast Cancer Trialists’ Collaborative Group (EBCTCG). Aromatase inhibitors versus tamoxifen in early breast cancer: patient-level meta-analysis of the randomised trials. Lancet 2015. doi:10.1016/S0140-6736(15)61074-1.