The Early Breast Cancer Trialists' Collaborative Group (EBCTCG) performed a comprehensive meta-analysis of 12 patient-level randomized trials. They involved more than 22,000 postmenopausal women with estrogen receptor-positive early breast cancer. The study provides compelling evidence supporting a statistical extension of aromatase inhibitor (AIT) treatment beyond 5 years. Allocation to AIT versus no other treatment reduced the recurrence of invasive breast cancer by 27% (RR 0.73; 95% CI 0.67–0.80; p < 0.0001). This effect was greater after prior treatment with tamoxifen alone than after partial prior AIT. The reduction in recurrence was greater in studies with 5 years of AIT versus no additional AIT than in studies with 2–3 years of AIT.[4]