DISEASE CHARACTERISTICS:

• Histologically confirmed nonmetastatic primary invasive adenocarcinoma of the breast

  • Adequately excised
  • Axillary nodes positive or negative
  • No positive or suspicious internal mammary nodes identified by sentinel node technique that have not been irradiated
  • No supraclavicular lymph node involvement

• HER2-positive disease with one of the following:

  • 3+ overexpression by immunohistochemistry (IHC)
  • 2+ overexpression by IHC and fluorescence in situ hybridization (FISH) with c-erbB2 gene amplification
  • c-erbB2 gene amplification by FISH
• Previously treated with at least 3 months or 4 courses of approved neoadjuvant or adjuvant chemotherapy with or without radiotherapy
• No synchronous bilateral or multifocal breast cancer that is not HER2-positive
• No locally advanced or inflammatory breast cancer
• No clinical T4 primary breast tumor
• Prior curatively treated ipsilateral ductal carcinoma in situ of the breast is allowed

• Hormone receptor status:

  • Estrogen receptor and progesterone receptor status known OR
  • Estrogen receptor status known

PATIENT CHARACTERISTICS:

Age

• 18 and over

Sex

• Female

Menopausal status

• Not specified

Performance status

• ECOG 0-1

Life expectancy

• Not specified

Hematopoietic

• WBC at least 2,500/mm^3
• Absolute neutrophil count at least 1,500/mm^3
• Platelet count at least 100,000

Hepatic

• Bilirubin no greater than 2 times upper limit of normal (ULN)
• AST and ALT no greater than 2.5 times ULN
• Alkaline phosphatase no greater than 2.5 times ULN

Renal

• Creatinine no greater than 2 times ULN

Cardiovascular

• LVEF at least 55% by echocardiography or MUGA
• No serious cardiac illness
• No documented congestive heart failure
• No high-risk uncontrolled arrhythmias
• No angina pectoris requiring antianginal medication
• No clinically significant valvular heart disease
• No evidence of transmural infarction on EKG
• No poorly controlled hypertension (i.e., systolic greater than 180 mm Hg or diastolic greater than 100 mm Hg)

Pulmonary

• No severe pulmonary disease/illness

Other

• No other malignancy except for curatively treated basal cell or squamous cell skin cancer, carcinoma in situ of the cervix, or other cancer that has been curatively treated, with no evidence of disease, and has less than 15% risk of recurrence over the next 10 years
• No other concurrent serious disease that would preclude study participation
• Not pregnant or nursing
• Negative pregnancy test
• Fertile patients must use effective barrier contraception

PRIOR CONCURRENT THERAPY:

Biologic therapy

• No prior peripheral stem cell or bone marrow stem cell transplantation as part of prior neoadjuvant or adjuvant chemotherapy regimen
• No prior biologic therapy or immunotherapy for breast cancer
• No prior anti-HER2 therapy for any reason
• No concurrent immunotherapy for breast cancer

Chemotherapy

• See Disease Characteristics
• See Biologic therapy
• No prior cumulative dose of doxorubicin more than 360 mg/m^2 or epirubicin more than 720 mg/m^2
• No prior anthracyclines for another malignancy
• No more than 7 weeks since day 1 of last chemotherapy course
• No concurrent adjuvant chemotherapy

Endocrine therapy

• No concurrent hormonal therapy, including aromatase inhibitors, pure antiestrogens, or progestational agents, for breast cancer
• Concurrent systemic adjuvant hormonal therapy for estrogen receptor-positive patients allowed
• Concurrent tamoxifen allowed

Radiotherapy

• See Disease Characteristics
• No more than 6 weeks since completion of prior radiotherapy
• No prior mediastinal irradiation except for internal mammary node irradiation for the present breast cancer

Surgery

• See Disease Characteristics
• No more than 6 weeks since prior definitive surgery
• Concurrent ovarian ablation allowed

Other

• No other concurrent investigational therapy for breast cancer
• Concurrent bisphosphonate therapy allowed if started prior to study