Inclusion Criteria

DISEASE CHARACTERISTICS:

- Histologically confirmed breast cancer

- Metastatic disease, defined by the existence of a secondary tumor localization
radiologically (i.e., by radiography, CT scan, MRI scan, or ultrasound) or
scintigraphically confrimed

- Evaluable disease

- Beginning first-line metastatic treatment with trastuzumab (Herceptin®) with or
without chemotherapy

- Primary tumor must overexpress HER2 (IHC 3+ OR IHC 2+ and FISH+ OR FISH+)

- Hormone receptor status not specified

- No brain metastasis

PATIENT CHARACTERISTICS:

- Menopausal status not specified

- Life expectancy > 3 months

- Able to undergo cardiotoxicity evaluation every 4 months by measuring LVEF via an
isotopic method or ultrasound with systematic registration

- No chronic uncontrolled disease

- No heart failure

- No respiratory failure or hypoxemia

- No history of another primary cancer except for basal cell carcinoma of the skin

- No severe uncontrolled infection

- No psychological incapacity

PRIOR CONCURRENT THERAPY:

- See Disease Characteristics