ESR1 and breast cancer: Comparing the highest versus lowest tertiles, ER expression in normal TDLUs was non-significantly but inversely associated with subsequent risk (odds ratio (OR)=0.44, 95% confidence interval (CI)=0.17–1.14, P trend=0.68), whereas Ki67 expression was non-significantly but positively associated with subsequent breast cancer risk (OR=1.59, 95% CI=0.80–3.14, P trend=0.48; Table 1).