ESR1 and breast cancer: However, in women with ER-positive tumors, the ER/PR/HER2 score was positively associated with breast cancer-specific mortality risk (Ptrend = 0.001; Figure 4A); the HR for breast cancer death was 2.48 (95% CI = 1.36 to 4.55) for those in the highest quartile of the ER/PR/HER2 score compared with those in the lowest quartile.