Compared with bone metastatic breast cancer patients who had ER-positive/PR-positive primary tumor, those with ER-positive/PR-negative (HR = 1.48, 95% CI: 1.37–1.62), ER-negative/PR-positive (HR = 2.45, 95% CI: 1.55–3.87), and ER-negative/PR-negative (HR = 1.95, 95% CI: 1.75–2.18) breast cancers showed poorer BCSS (all log-rank p < 0.001, Figure 2C). Here, ESR1 is linked to breast carcinoma.