Capecitabine and Pegylated Interferon Alfa-2a in Treating Patients With Recurrent or Progressive Brain Metastases Due to Breast Cancer

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