Food and Drug Administration (FDA) Good Clinical Practices (GCPs), and local ethical and legal requirements. 4.0 MATERIALS AND METHODS 4.1 Patients Patients over the age of 18 years with a diagnosis of HER2-positive breast cancer who are receiving neoadjuvant therapy with an approved regimen that includes trastuzumab and do not achieve a pathologic complete response or who undergo upfront surgery and are found to be pathologically node-positive will be targeted. Patients treated with neoadjuvant therapy must receive an approved regimen that includes trastuzumab and at least four cycles (12 weeks) of taxane- containing chemotherapy. These patients will be approached after their surgical pathology report is available and confirms residual disease.