In patients with adjuvant-stage estrogen receptor–negative, progesterone receptor–negative breast cancer, multivariate Cox regression results showed worse OS (hazard ratio, 1.27; 95% CI, 1.06-1.51; P = .008) and worse CSS (hazard ratio, 1.26; 95% CI, 1.04-1.52; P = .02) for patients residing in rural areas. Here, ESR1 is linked to breast cancer.