ESR1 and breast cancer: Within separate categories of HRT use, we observed a positive risk association within the third tertile of BMI with ER-PR- breast cancer among never users of HRT (third versus first tertile HR = 1.47 (95%CI: 1.01 to 2.15); Ptrend = 0.06) (Table 4) contrasted by an indication of a negative risk association among current and no association with past users of HRT.