ESR1 and breast cancer: In contrast, there was no statistically significant difference in BCSS between ER-negative/PR-positive and ER-negative/PR-negative breast cancers (HR = 0.83, 95% CI: 0.59–1.14, log-rank p = 0.207, Figure 2C), and the same difference trend was found in OS of bone metastatic breast cancer subgroups with four HR statuses (Figure 2D).