ERBB2 and aneurysmal bone cyst: In the multivariable model including patients with HER2 + ABC, the following variables had a significant (≤ 0.05) or borderline significant (≤ 0.10) impact on OS: age at ABC diagnosis (hazard ratio per year 1.01, 95% CI 1.01–1.02), WHO performance status ≥ 2 (hazard ratio 2.29, 95% CI 1.58–3.32), WHO performance status unknown (hazard ratio 1.61, 95% CI 1.27–2.05), multiple initial metastatic sites (hazard ratio 1.68, 95% CI 1.25–2.25), and MFI 3–23 months (hazard ratio 1.56, 95% CI 1.12–2.19) (Table 2).