CYP19A1 and breast cancer: However, HER2-negative BC patients derived benefit from aromatase inhibitor (5.4% absolute benefit in DFS at 8 years, HR 0.70), whereas tamoxifen was numerically superior in the HER2-positive subgroup (n = 695, 3.2% difference in DFS at 8 years, HR 1.18, 95% CI 0.80–1.73)22.