CYP19A1 and breast cancer: In premenopausal patients with HR-positive BC undergoing ovarian function suppression (OFS), an aromatase inhibitor is superior to tamoxifen as demonstrated by the TEXT and SOFT trials, with a delta in distant disease-free survival (DFS) at 8 years of 4% (HR 0.77, 95% CI 0.67–0.90)22.