In the unadjusted analysis, the ER-positive/PR-negative (HR, 1.67; 95% CI, 1.64-1.70) and ER-negative/PR-positive (HR, 1.83; 95% CI, 1.74-1.92) subtypes had a higher risk of BC-specific death than the ER-positive/PR-positive subtype (Figure 3B). This evidence concerns the gene ESR1 and breast cancer.