ERBB2 and breast cancer: Human epidermal growth factor receptor 2 (HER2)-positive breast cancer accounts for ~15–20% of all breast cancer cases and is characterized by high malignancy and poor prognosis until the introduction of HER2-targeted therapies.1 Anti-HER2 therapy significantly improves the survival of these patients.2,3 With the continuous progress of medical research, anti-HER2 therapeutic drugs, including monoclonal antibodies, tyrosine kinase inhibitors (TKIs), and antibody-conjugated drugs (ADCs), continue to emerge.