DISEASE CHARACTERISTICS: Histologically confirmed stage IV breast cancer that overexpresses HER2/neu Evidence of at least a partial response (at least 50% reduction) to salvage chemotherapy as initial chemotherapy for metastatic disease Measurable disease not required if there is no disease progression at induction chemotherapy Bone lesions as only site of metastatic disease allowed if evidence of clinical improvement and no new lesions on x-ray No CNS metastases Hormone receptor status: Not specified