ESR1 and breast cancer: A systematic review on the risk of intrinsic BC tumor subtypes, including 38 studies with pre- and postmenopausal BC cases and controls among Caucasian and Asian women, concluded that most established risk factors reflect risk factors for luminal A (ER+ and/or PR+, HER2−) BC and that some BC risk factors may be differentially associated with other intrinsic tumor subtypes17.