This retrospective NHS2 cohort study in largely White non-Hispanic women validates earlier CTS findings and confirms that women with preeclampsia who have inherited the common T allele of IGF1R rs2016347 have a 30–40% lower risk of developing HR+ breast cancer, pointing to the need to consider incorporating this exposure information (preeclampsia history and IGF1R rs2016347 genotyping) into risk assessment models and personalized breast cancer screening recommendations. Here, IGF1R is linked to breast cancer.