ESR1 and breast cancer: When classifying ER-positive patients by tumor size and grade alone into three groups (of increasing tumor size and grade), the absolute 10-year risks of breast cancer death were 3.0% (95% CI 1.3% to 4.7%), 7.1% (95% CI 4.7% to 9.5%), and 12.2% (95% CI 6.3% to 17.8%) among those treated and 5.1% (95% CI 3.3% to 6.9%), 10.5% (95% CI 7.7% to 13.3%), and 15.9% (95% CI 9.6% to 21.7%) among those untreated.