ESR1 and breast cancer: Although studies evaluating the relationship between BC and levels of this trans fatty acid in biomarkers are scarce, positive associations have been described in the serum of current postmenopausal smokers [56], in the erythrocytes membrane of overweight/obese women from the Nurses’ Health Study II [17], and in the plasma of a cohort of Australian women, although in the latter case the association was only found with ER-/PR- tumors [16].