DISEASE CHARACTERISTICS: Histologically confirmed recurrent or metastatic breast cancer HER2-neu overexpressing tumor (2+ or 3+) Measurable or evaluable disease If bone disease only, must have lytic lesions No carcinomatous meningitis or untreated or uncontrolled brain parenchymal disease Prior brain parenchymal disease allowed if controlled by appropriate therapy given at least 8 weeks prior to study, and patient is asymptomatic from CNS disease Hormone receptor status: Not specified