ERBB2 and bone metastasis: Bone metastasis incidence was significantly higher in the HER2-low subgroup (62.0% vs. 37.0%, p = 0.024), while no notable between-group differences emerged in other metastatic sites, treatment lines (≥3 lines: 76.1% vs. 64.0%, p = 0.266), or combination therapy (67.4% vs. 60.0%, p = 0.527).