RATIONALE: Studying samples of blood and DNA in the laboratory from patients who received chemotherapy with or without trastuzumab may help doctors learn more about the effects of trastuzumab on cells. It may also help doctors understand how well patients respond to treatment.

PURPOSE: This research trial studies blood and DNA samples from patients with breast cancer treated with chemotherapy with or without trastuzumab.

OBJECTIVES:

• To determine the role of trastuzumab in the generation of HER2-specific antibodies in breast cancer patients undergoing adjuvant combination therapy.
• To determine whether the improved disease-free period and overall survival of patients treated in the adjuvant setting with combination of chemotherapy and trastuzumab is dependent on the Fcγ receptor genotype of the patient.

OUTLINE: Previously collected serum and DNA samples are analyzed for HER2-specific antibodies and FcγR genotype by enzyme-linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR).

• Patients with HER-2-overexpressing node-positive or high-risk node-negative breast cancer enrolled on NCCTG-N9831

* Pre- and post-treatment serum and DNA samples of patients treated with doxorubicin and cyclophosphamide followed by paclitaxel with or without trastuzumab (Herceptin®)

Patients enrolled on NCCTG-N9831.