ESR1 and breast cancer: According to a collaborative meta-analysis of individual patient data from 20 trials (n = 21,457) in early breast cancer of about 5 years of tamoxifen versus no adjuvant tamoxifen by Early Breast Cancer Trialists’ Collaborative Group [4], the rate ratios were 0.63 (standard error, 0.03) for ER+/PgR+ disease (P <0.00001) but 0.90 (standard error, 0.10) for ER–/PgR+ disease (P = 0.35).