In breast cancer, it is an established prognostic and predictive biomarker.1 Where the adjuvant management of early HER2-positive breast cancer is concerned, significant improvements in disease-free and overall survival have been shown with the addition of trastuzumab to chemotherapy for tumors > 1 cm and for node-positive disease.2-6 This benefit was also seen for tumors < 1 cm when certain adverse prognostic features were present.7 The gene discussed is ERBB2; the disease is breast cancer.