ESR1 and breast cancer: Concerning PFOS and PFOA, by applying single-pollutant models on data from the E3N cohort data, a positive linear association between circulating level of PFOS and estrogen receptor positive (ER +) breast cancer risks was highlighted, while a positive non-linear association was found between both PFOS and PFOA and estrogen receptor negative (ER-) breast cancer risk [18].