Besides clinically established predictive factors, such as tumor grade and size, hormone receptor (HR) status, lymph node involvement, human epidermal growth factor receptor 2 (HER2) status, and gene expression profiles, novel clinically relevant predictive and prognostic factors are needed to help inform personalization of adjuvant therapies and risk stratification of breast cancer patients. The gene discussed is ERBB2; the disease is breast carcinoma.