Inclusion Criteria

DISEASE CHARACTERISTICS:

- Histologically confirmed adenocarcinoma of the breast, meeting one of the following
criteria:

- Metastatic disease

- High-risk disease, defined as early-stage disease with pathologic involvement of
locoregional lymph nodes

- Patients who are/will be receiving standard adjuvant trastuzumab
[Herceptin®] for high-risk disease will participate in this study during
the single-agent trastuzumab portion of their therapy

- No clinical or radiographical evidence of active disease

- Not eligible for therapy of known curative potential for metastatic breast cancer

- HER2/neu-overexpressing disease, defined as HER2/neu positive by IHC 3+ staining or
by FISH+ amplification

- Stable CNS disease allowed provided it has been adequately treated and is not under
active treatment

- Hormone receptor status not specified

PATIENT CHARACTERISTICS:

- Menopausal status not specified

- ECOG performance status 0-1

- ANC > 1,000/mm^3

- Platelet count > 100,000/mm^3

- Serum creatinine < 2.0 mg/dL

- Serum bilirubin ≤ 2.0 mg/dL (unless elevation is due to known Gilbert's syndrome)

- AST/ALT ≤ 2 times upper limit of normal (ULN)

- Alkaline phosphatase ≤ 5 times ULN

- Not pregnant or nursing

- Negative pregnancy test

- Fertile patients must use effective contraception

- Cardiac ejection fraction normal by MUGA OR ≥ 45% by ECHO

- No other malignancies within the past 5 years, except for carcinoma in situ of the
cervix, superficial nonmelanoma skin cancer, or superficial bladder cancer

- No prior or currently active autoimmune disease* requiring management with systemic
immunosuppression, including any of the following:

- Inflammatory bowel disease

- Systemic vasculitis

- Scleroderma

- Psoriasis

- Multiple sclerosis

- Hemolytic anemia or immune-mediated thrombocytopenia

- Rheumatoid arthritis

- Systemic lupus erythematosus

- Sjögren syndrome

- Sarcoidosis

- Other rheumatologic disease

- No symptomatic intrinsic lung disease or extensive tumor involvement of the lungs
resulting in dyspnea at rest

- HIV-negative

- No evidence of active acute or chronic infection

- No uncontrolled medical problems

- No active major medical or psychosocial problems that could be complicated by study
participation

- No corn allergy

- No known severe hypersensitivity to trastuzumab (except for mild to moderate infusion
reactions that are easily managed and do not recur) NOTE: *Asthma or chronic
obstructive pulmonary disease that does not require daily systemic corticosteroids
allowed

PRIOR CONCURRENT THERAPY:

- Any number of prior chemotherapy regimens for metastatic breast cancer allowed

- Prior or concurrent trastuzumab in the adjuvant or metastatic setting allowed

- More than 28 days since prior and no concurrent systemic oral steroids

- Topical, ocular, or nasal steroids allowed

- More than 28 days since prior and no concurrent chemotherapy, radiotherapy, or
biologic therapy (except trastuzumab)

- More than 28 days since prior and no concurrent participation in another
investigational clinical trial involving a new drug

- Concurrent endocrine therapy or bisphosphonates allowed