CYP19A1 and breast cancer: A 5-year “upfront” endocrine therapy with an aromatase inhibitor was associated with a lower risk of breast cancer recurrence (10-year recurrence risk 19.1% versus 22.7%), as well as lower cases of death (RR 0.85; 95% CI, 0.75–0.96, p-value = 0.010), compared to 5 years of tamoxifen.