DISEASE CHARACTERISTICS:

          -  Histologically confirmed invasive breast cancer

          -  No evidence of metastatic disease

          -  Overexpression of HER2 receptor defined as 3+ or 2+ HER2 positivity measured by
             fluorescent in situ hybridization (FISH) gene amplification

          -  Indication for chemotherapy based on the following clinical and histopathological
             features:

               -  Receiving or scheduled to receive neoadjuvant chemotherapy

                    -  Time between diagnosis biopsy and start date of chemotherapy should be less
                       than 1 month

               -  Receiving or scheduled to receive adjuvant chemotherapy

                    -  Completely resected disease, with negative surgical margins (apart from deep
                       margin if full thickness resection)

                    -  Marginally resected disease and/or positive sentinel nodes allowed provided
                       patients undergo completion of surgery (breast and/or axillary clearance)
                       after chemotherapy

          -  Hormone receptor status known

        PATIENT CHARACTERISTICS:

          -  Menopausal status not specified

          -  ECOG performance status 0-1

          -  Adequate bone marrow, hepatic, and renal function

          -  LVEF normal by ECHO or MUGA

          -  Not pregnant or nursing

          -  Fertile patients must use effective contraception

          -  No clinically significant cardiac abnormalities

          -  No myocardial infarction within the past 6 months

          -  No uncontrolled or malignant hypertension

          -  No history of atrioventricular arrhythmia and/or congestive heart failure (even under
             medical control), or active second or third degree cardiac block

          -  No history of allergy to drugs containing polysorbate 20 and the excipient polysorbate
             80 (TWEEN 80®) or history of allergy to mouse proteins

          -  No co-morbidity significantly adding to risks associated with cytotoxic chemotherapy
             (i.e., severe chronic obstructive pulmonary disease or poorly controlled diabetes)

          -  No prior diagnosis of malignancy unless managed by surgical treatment only and
             disease-free for 10 years

               -  Prior basal cell carcinoma, cervical carcinoma in situ, or ductal carcinoma in
                  situ of the breast allowed if treated by surgery only

          -  No concomitant medical or psychiatric problems that might preclude completion of
             treatment or follow-up

        PRIOR CONCURRENT THERAPY:

          -  See Disease Characteristics

          -  No prior chemotherapy or radiotherapy

          -  Concurrent radiotherapy allowed