ERBB2 and breast cancer: Human epidermal growth factor receptor 2 (HER2) is a well-recognized oncogenic driver that functions across a variety of tumor types.1–4 HER2 alteration is associated with inferior prognosis in breast cancer, gastric cancer, and lung cancer.5–8 As a clinically actionable genetic abnormality, HER2-targeted monoclonal antibodies (mAbs) or tyrosine kinase inhibitors (TKIs) have substantially extended survival in patients with HER2-positive breast cancer and gastric cancer.9–13 Disappointingly, the advantageous effects of these targeted therapies were largely not extended to lung cancer.