ESR1 and breast carcinoma: There were significant differences in stage_N (P = 0.014), histological grade (P = 0.001), ER status (P < 0.001), PgR status (P < 0.001), NACT regimens (P = 0.032) and NACT efficacy (P = 0.037) between patients with HER2-negative and HER2-low breast cancer.