ERBB2 and breast cancer: The risk of BM has been shown to correlate with breast cancer subtype, and patients with triple negative or Human epidermal growth factor receptor-2 (HER2)-positive subtypes experience significantly higher BM occurrence than patients with luminal-like disease [6–10], having a 3.5–3.6 fold increased risk compared with that of luminal tumors [2, 9, 11].