Several gene expression profiling (GEP) tests including EndoPredict® (EPclin score), Oncotype DX® Breast Recurrence Score and Prosigna® are approved to guide adjuvant chemotherapy decisions for patients with oestrogen receptor (ER)-positive, human epidermal growth factor receptor 2 (HER2)-negative and lymph node (LN)-negative breast cancer. The gene discussed is ERBB2; the disease is breast cancer.