ERBB2 and breast cancer: human epidermal growth factor receptor 2 (HER2) positive breast cancer accounts for 15% to 20% of all breast cancer cases.[1] Compared with other subtypes, HER2 positive breast cancer is characterized by a poorer prognosis and predispose patients to brain metastasis.[2] Management of HER2 positive patients using HER2 inhibitors has greatly improved the overall prognosis.