ESR1 and breast cancer: In particular, Aft et al. [20] demonstrated that patients with DTC-free BC treated with monthly ZA were more likely to remain DTC-free at 3 months (P = 0.03), and that the subset of patients with estrogen receptor (ER)-negative and human epidermal growth factor receptor 2 (HER-2)-negative disease were more likely to have pathologic complete response with ZA versus no ZA.