Additional factors associated with increased breast cancer–specific mortality were non-Hispanic Black race (HR, 1.70; 95% CI, 1.26-2.30; P < .001) and aggressive tumor subtype (ER-negative/ERBB2-negative) (HR, 2.07; 95% CI, 1.67-2.56; P < .001) (Table 3). This evidence concerns the gene ESR1 and breast cancer.