In postmenopausal women, the majority of studies find a positive association between overweight and risk of estrogen receptor positive (ER+)/progesterone receptor positive (PR+) breast cancer [5, 9], especially in women who have not used hormone replacement therapy (HRT) [4, 10–13], whereas results are conflicting regarding the risk of triple negative breast cancer (TNBC) [4, 5, 12, 14]. Here, ESR1 is linked to breast cancer.