Inclusion Criteria

DISEASE CHARACTERISTICS:

- Histologically or cytologically confirmed breast cancer that metastasized to the
brain, meeting all of the following criteria:

- Must have ≥ 1 inoperable brain metastases, meeting 1 of the following criteria:

- Progressive or recurrent disease after prior whole-brain or stereotactic
radiotherapy

- Ineligible for OR unwilling to be treated with radiotherapy

- At least 1 unidimensionally measurable brain metastasis by enhanced MRI within
the past 21 days

- No progression or development of central nervous system (CNS) metastasis during
prior treatment with capecitabine, fluorouracil, interferon alfa, or interferon
beta

- Systemic (i.e., outside the CNS system) cancer must be stable

- No progressive disease (e.g., liver, lymphangitic, or lung metastases)

- Hormone receptor status:

- Not specified

PATIENT CHARACTERISTICS:

Age

- 18 and over

Sex

- Male or female

Menopausal status

- Not specified

Performance status

- Karnofsky 70-100%

Life expectancy

- More than 12 weeks

Hematopoietic

- Absolute neutrophil count ≥ 1,500/mm^3

- Platelet count ≥ 100,000/mm^3

- Hemoglobin ≥ 10 mg/dL

- No history of idiopathic thrombocytopenic purpura

- No known uncontrolled coagulopathy

- No increased risk for anemia (e.g., thalassemia or spherocytosis)

- No medically problematic anemia

Hepatic

- aspartate aminotransferase (AST or SGOT) and alanine aminotransferase (ALT or SGPT) ≤
2.5 times upper limit of normal (ULN) (5 times ULN for patients with concurrent liver
metastases )

- Bilirubin ≤ 1.5 times ULN

- Alkaline phosphatase ≤ 2.5 times ULN (5 times ULN for patients with concurrent liver
metastases; 10 times ULN for patients with concurrent bone metastases)

Renal

- Creatinine ≤ 1.5 times ULN OR

- Creatinine clearance ≥ 30 mL/min

Cardiovascular

- No congestive heart failure

- No symptomatic coronary artery disease

- No medically uncontrolled arrhythmia

- No other clinically significant cardiac disease

- No myocardial infarction within the past 12 months

Gastrointestinal

- No history of inflammatory bowel disease

- Must have intact upper gastrointestinal tract

- Able to swallow tablets

- No malabsorption syndrome

- No history of gastrointestinal bleeding

Immunologic

- No prior unanticipated severe reaction to fluoropyrimidine therapy, interferon,
pegylated interferon, or a pegylated moiety

- No known sensitivity to fluorouracil

- No serious uncontrolled infection

- No history of immunologically mediated disease

Other

- Not pregnant or nursing

- Negative pregnancy test

- Fertile patients must use effective contraception during and for 6 months after
completion of study treatment

- No known dihydropyrimidine dehydrogenase deficiency

- No history of depression characterized by a suicide attempt

- No history of hospitalization for psychiatric disease

- No history of other severe psychiatric disease

- No prior disability as a result of psychiatric disease

- No history of clinically significant psychiatric disability that would preclude study
compliance

- No other malignancy within the past 5 years except cured nonmelanoma skin cancer or
treated carcinoma in situ of the cervix

- No uncontrolled thyroid dysfunction (e.g., thyroid-stimulating hormone not in normal
range)

- No evidence of severe retinopathy (e.g., Cytomegalovirus (CMV) retinitis or macular
degeneration)

- No clinically relevant ophthalmologic disorders due to diabetes or hypertension

- No other serious uncontrolled medical conditions that would preclude study
participation

PRIOR CONCURRENT THERAPY:

Biologic therapy

- See Disease Characteristics

- At least 3 months since prior interferon alfa or interferon beta

Chemotherapy

- See Disease Characteristics

- At least 3 months since prior capecitabine or fluorouracil

Endocrine therapy

- Concurrent hormonal agents (e.g., tamoxifen, raloxifene, or anastrazole) for breast
cancer allowed

Radiotherapy

- See Disease Characteristics

Surgery

- More than 4 weeks since prior major surgery and recovered

Other

- More than 4 weeks since prior participation in another investigational drug study

- At least 4 weeks since prior and no concurrent brivudine or sorivudine

- No concurrent cimetidine

- No other concurrent investigational or commercial agents or therapies for this
malignancy