ERBB2 and breast cancer: Trastuzumab therapy improves the prognosis of patients with HER2-positive breast cancer; thus, the causes and consequences of interrupting this treatment due to cardiotoxicity must be better understood to improve the clinical management of these patients.(13) Therefore, the objectives of this study were to analyze the prognosis of breast cancer patients who developed cardiotoxicity induced by adjuvant trastuzumab therapy and to analyze factors associated with and resulting from cardiotoxicity.