DISEASE CHARACTERISTICS: Histologically confirmed metastatic adenocarcinoma of the breast Must have failed at least one but no more than two prior therapies for metastatic breast cancer, including endocrine and chemotherapy Relapsing while receiving or within 6 months of completing adjuvant chemotherapy Disease progression during or subsequent to the most recent therapy Measurable and evaluable disease Bone is an evaluable site only No CNS metastases Hormone receptor status: Estrogen receptor negative, positive, or unknown