Among incident cases with known subtype defined by estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2) [1], luminal A (ER-positive and/or PR-positive and HER2-negative) is the most common subtype, accounting for 72.7% of breast cancers, with the highest incidence among non-Hispanic White (NHW) women. Here, ESR1 is linked to breast cancer.