DISEASE CHARACTERISTICS: Histologically proven stage IV epithelial breast cancer Must meet one of the following conditions: Complete or partial remission or stable disease following chemotherapy or radiotherapy Previously untreated disease No progressive disease after prior therapy for metastatic breast cancer Overexpression of HER2 protein (2+ or 3+ by immunohistochemistry) allowed if failed prior trastuzumab (Herceptin) therapy Measurable disease by physical exam or external imaging studies OR Evaluable disease (e.g., abnormal bone scan) Availability of a suitable HLA-A, B, and DR phenotypically identical sibling donor No active CNS disease Hormone receptor status: Not specified