ESR1 and breast cancer: At a median follow-up of 8 years, adding tamoxifen to radiation therapy after lumpectomy reduced distant recurrence by 1.8% in absolute value, without statistical significance. Moreover, the integrated analysis for ER-positive T1a/bN0M0 breast cancer from three randomized studies (NSABP-B06, B-14, and B-20) revealed that adjuvant tamoxifen improved recurrence-free survival than surgery alone (HR, 0.55; 95% CI, 0.35–0.88) [22].