In multivariable regression, rural patients with adjuvant-stage estrogen receptor–negative and progesterone receptor–negative breast cancer had worse overall survival (hazard ratio, 1.27; 95% CI, 1.06-1.51; P = .008) and cancer-specific survival (hazard ratio, 1.26; 95% CI, 1.04-1.52; P = .02). Here, ESR1 is linked to breast cancer.