ESR1 and breast cancer: With regard to postmenopausal HRT use, Cox regression models showed that in comparison to HRT never users, postmenopausal women who were current HRT users at baseline had significantly increased risks of both ER-PR- breast cancer (HR = 1.30 (95%CI: 1.05 to 1.62); Pvalue = 0.02) and ER+PR+ breast cancer (HR = 1.74 (95%CI: 1.56 to 1.95); Pvalue < 0.001), although the relative risk was significantly weaker for ER-PR- than for ER+PR+ tumors (Phet = 0.035).