CYP19A1 and breast cancer: Furthermore, in a previous cohort study, the Early Breast Cancer Trialists’ Collaborative Group (EBCTCG) reported that 5-year adjuvant tamoxifen and aromatase inhibitors reduced recurrence risk for ER-positive breast cancer, including T1 disease (tamoxifen vs. control: rate ratio [RR], 0.60 and aromatase inhibitors vs. tamoxifen: RR 0.76) [23–25].