50-year-old women with early HER- 2/neu-positive breast cancer, who had successfully completed a surgical resection of disease. Patients entered the model in the postsurgical with trastuzumab or postsurgical without trastuzumab states, depending on the presence or absence of pre-existing low left ventricular ejection fraction (LVEF). The gene discussed is ERBB2; the disease is breast carcinoma.