ESR1 and breast cancer: Moreover, after adjusting for the covariates, compared with the ER-positive/PR-positive bone metastatic breast cancers, the ER-positive/PR-negative, ER-negative/PR-positive, and ER-negative/PR-negative subgroups were statistically associated with 51% (HR = 1.51, 95% CI: 1.40–1.64), 232% (HR = 3.32, 95% CI: 2.46–4.47), and 151% (HR = 2.51, 95% CI: 2.28–2.75) increased risks of breast cancer specific death respectively, and 47% (HR = 1.47, 95% CI: 1.37–1.58), 241% (HR = 3.41, 95% CI: 2.59–4.49), and 148% (HR = 2.48, 95% CI: 2.27–2.71) increased risks of overall death.