ESR1 and breast cancer: 5-years invasive relapse-free survival (iRFS) was 73.9% (95% confidence interval (95% CI) = 69.0–79.2%) in the whole population, 74.0% (95% CI = 68.8–79.6%) for patients with ER-negative BC and 73.1% (95% CI = 59.3–90.2%) for patients with ER-low positive BC.