ESR1 and aneurysmal bone cyst: In multivariate analyses, ER-negative status (HR 1.79; 95% CI: 1.29–2.48), bone metastases at the initiation of first-line chemotherapy (HR 1.51; 95% CI: 1.10–2.07), liver metastases at the initiation of first-line chemotherapy (HR 1.61; 95% CI: 1.14–2.28), a disease-free interval <24 months (HR 1.39; 95% CI: 1.04–1.87), and perioperative anthracycline- and/or taxane-based regimen (HR 1.66; 95% CI: 1.23–2.24) were all associated with poor OS, indicating that they are prognostic factors for HER2− ABC patients undergoing first-line chemotherapy.