ESR1 and breast cancer: Our finding is consistent with a previous study of women with atypical hyperplasia that reported a fourfold higher breast cancer risk associated with Ki67 expression (⩾2 vs. <2%)4 and experimental studies that suggested carcinogenic potentials of PR.8 However, we did not observe a positive association with ER despite the supporting evidence.9,10 This study has limitations including potential measurement error in markers (for example, lack of data on menstrual phase, moderate correlations between automated and manual scores), which would bias results towards the null.