Molecular approaches to clinical diagnostics and treatment of breast cancer first came into clinical practice some 20 years ago following the development of the immunohistochemistry (IHC) test for the detection of human epidermal growth factor receptor 2 (HER2/ERBB2/NEU), but the number of validated protein biomarkers in clinical diagnostics remains low. The gene discussed is ERBB2; the disease is breast carcinoma.