- Patients with histologically confirmed adenocarcinoma of the breast which is metastatic and is known to overexpress HER2/neu who have received no prior chemotherapy for metastatic breast cancer; prior hormonal therapy for metastatic disease is allowed; NOTE: for this protocol, HER2 overexpression will be defined as 3+ HER2 positivity as measured by immunohistochemistry using the HercepTest (DAKO) or HER2 gene amplification as measured by fluorescent in-situ hybridization (FISH, e.g. Vysis); representative diagnostic tissue must be submitted for central diagnostic review