In HER2-negative bone metastatic breast cancers, the BCSS was still best in the ER-positive/PR-positive breast cancers (Figure 3B); the ER-positive/PR-negative (HR = 1.72, 95% CI: 1.55–1.91), ER-negative/PR-positive (HR = 3.58, 95% CI: 1.76–7.30), and ER-negative/PR-negative (HR = 2.92, 95% CI: 2.52–3.39) breast cancers manifested poorer BCSS (Figure 3D). Here, ESR1 is linked to breast cancer.