ESR1 and breast cancer: In the BCSS status analysis, MRM, larger tumor size, lymph node involvement, high histological grade, hormone therapy other than tamoxifen, and chemotherapy were significantly associated with an increased risk of BC-specific mortality in the univariate analysis (Table 2); alternatively, ER (HR, 0.56; 95% CI 0.32–0.98; p = 0.042) and PgR (HR, 0.347; 95% CI, 0.196–0.616; p < 0.001) expression significantly reduced the risk.