ESR1 and breast carcinoma: In a multiethnic cohort of breast cancer survivors, women with ER negative breast cancer had significantly lower serum 25OHD than those with ER positive tumors [24], and in a case-control study with both pre- and postmenopausal women, reduced risk of breast cancer with higher 25OHD levels was found only among women with ER-/PR- tumors [26].