RATIONALE: Measuring blood levels of tumor cells in patients with breast cancer may help doctors predict how patients will respond to treatment.

PURPOSE: This laboratory study is looking at blood levels of tumor cells in predicting response in patients receiving first-line chemotherapy for stage IV breast cancer.

OBJECTIVES:

Primary

• Predict the overall and progression-free survival of patients with stage IV breast cancer by measuring the rate of circulating tumor cells (CTC) before the second course of chemotherapy.

Secondary

• Predict overall and progression-free survival of these patients by measuring the rate of CTC before the start of chemotherapy, at the first tumor evaluation, and after 2-3 courses of chemotherapy.
• Correlate the detection of CTC with tumor markers, clinical response, and radiological response.
• Study the changing status of HER-2 in CTC in patients receiving trastuzmab (Herceptin®).

OUTLINE: This is a multicenter study.

Blood samples are collected at baseline, before the second course of chemotherapy, before the third or fourth course of chemotherapy, and when progressive disease is diagnosed (before second-line treatment is initiated). Circulating tumor cells from the blood samples are examined by immunofluorescence.

Patients are followed periodically for up to 3 months.

DISEASE CHARACTERISTICS:

• Diagnosis of stage IV breast cancer
• Measurable or evaluable disease
• Scheduled to receive first-line chemotherapy with or without trastuzumab (Herceptin®), depending on HER-2 status
• Histologic block available for confirming pathologic diagnosis and measuring HER-2 status via FISH

PATIENT CHARACTERISTICS:

• Life expectancy > 3 months
• No other cancer in the past 5 years except for basal cell skin cancer or epithelial in situ cancer of the cervix
• No geographic, social, or psychiatric reasons that would make treatment impossible

PRIOR CONCURRENT THERAPY:

• No prior chemotherapy for metastatic disease