ESR1 and breast cancer: A slight increase in risk for ER+PR+ breast cancer and a reduced risk for ER- PR- breast cancer was observed with increasing age at first full-term pregnancy, but none of the confidence limits for the risk estimates excluded 1.0 and no linear trend in risk was observed for either cancer type (ER+PR+, ptrend = 0.49; ER- PR-, ptrend = 0.08; Table 2).