ERBB2 and breast cancer: Compared to patients with single BM, those with multiple BM were more likely to have infratentorial BM (adjusted odds ratio [aOR] 3.35, 95% confidence interval [CI] 1.03–10.83, p = 0.044), HER2(human epidermal growth factor receptor 2)-positive BC (aOR 3.93, 95% CI 1.23–12.53, p = 0.021) and hepatic metastases (aOR 5.86, 95% CI 1.34–25.61, p = 0.019).