DISEASE CHARACTERISTICS:

• Histologically confirmed metastatic adenocarcinoma of the breast

  • Patients may have had or not had standard first-line chemotherapy for the treatment of metastatic disease
• Overexpression of HER2-neu (HER2 3+ by immunohistochemistry or gene amplification as measured by fluorescent in situ hybridization)
• Measurable disease
• Patients with no prior adjuvant chemotherapy may have failed or not failed first-line chemotherapy for metastatic disease

• No more than 2 prior systemic chemotherapy regimens for metastatic disease

  • Relapse while receiving or within 6 months of completion of adjuvant chemotherapy is considered failure of 1 regimen for metastatic disease

• No untreated brain metastases or brain metastases undergoing radiotherapy

  • Previously treated brain metastasis that has responded to radiotherapy and/or surgery allowed if not sole site of measurable disease

• Hormone receptor status:

  • Not specified

PATIENT CHARACTERISTICS:

Age:

• 18 and over

Sex:

• Male or female

Menopausal status:

• Not specified

Performance status:

• ECOG 0-2

Life expectancy:

• Not specified

Hematopoietic:

• Granulocyte count at least 1,500/mm^3
• Platelet count at least 100,000/mm^3

Hepatic:

• Bilirubin no greater than 1.5 times upper limit of normal (ULN)
• AST and ALT no greater than 3 times ULN (5 times ULN if liver metastases is present)
• INR no greater than 1.5 times ULN
• PT and PTT no greater than 1.5 times ULN

Renal:

• Creatinine no greater than 1.5 mg/dL
• No more than trace blood or protein in urine

Cardiovascular:

• LVEF ≥ 50% by MUGA scan
• No prior New York Heart Association class I-IV heart disease
• No PR prolongation or atrioventricular block on ECG

Other:

• Not pregnant or nursing
• Negative pregnancy test
• Fertile patients must use effective contraception (preferably nonhormonal)
• Random blood sugar less than 2.5 times ULN
• No other malignancy within the past 5 years except curatively treated basal cell or squamous cell skin cancer or carcinoma in situ of the cervix
• No other acute or chronic medical or psychiatric condition or laboratory abnormality that would preclude study participation

PRIOR CONCURRENT THERAPY:

Biologic therapy:

• No prior trastuzumab (Herceptin)
• No other concurrent immunologic therapy

Chemotherapy:

• See Disease Characteristics
• Recovered from prior cytotoxic chemotherapy
• No prior cumulative dose of doxorubicin more than 360 mg/m^2
• No concurrent chemotherapy

Endocrine therapy:

• At least 2 weeks since prior hormonal therapy
• No concurrent hormonal therapy, including tamoxifen
• No concurrent dexamethasone, progesterone, or glucocorticoids

Radiotherapy:

• See Disease Characteristics
• At least 2 weeks since prior radiotherapy
• No prior radiotherapy to target lesions or only site of measurable disease
• No concurrent radiotherapy

Surgery:

• See Disease Characteristics
• No prior organ allograft

Other:

• No prior gefitinib
• No prior immunosuppressive therapy
• At least 2 weeks since prior cytotoxic drugs
• No concurrent carbamazepine, ethosuximide, griseofulvin, nafcillin, nelfinavir mesylate, nevirapine, oxcarbazepine, phenobarbital, phenylbutazone, phenytoin, primidone, rifabutin, rifampin, rofecoxib, Hypericum perforatum (St. John's Wort), sulfadimidine, sulfinpyrazone, troglitazone, or grapefruit juice
• No other concurrent investigational agents
• No concurrent topical eye agents
• Concurrent bisphosphonates allowed for hypercalcemia and/or prophylaxis of bone metastases