Women in the highest quintile of exposure (≥74.9 Bq/m3) had a suggested elevated risk of ER- (adjusted HR = 1.34, 95% CI: 0.97, 1.86, p for trend = 0.15), ER−/PR- breast cancer (adjusted HR = 1.38, 95% CI: 0.97, 1.96, p for trend = 0.05), and ER−/PR−/HER2- breast cancer (adjusted HR = 1.52, 95% CI: 0.96, 2.41, p for trend = 0.02) compared to women in the lowest quintile (<27.0 Bq/m3) in fully adjusted models. This evidence concerns the gene ESR1 and breast cancer.