Inclusion Criteria

DISEASE CHARACTERISTICS:

- Histologically or cytologically confirmed diagnosis of adenocarcinoma of the breast

- Evidence of metastatic involvement (stage IV disease)

- Patients must have measurable disease

- At least one measurable lesion as defined by the Response Evaluation Criteria in
Solid Tumors (RECIST)

- Treated brain metastases (surgery or radiation therapy) allowed if clinically stable

- Patients with leptomeningeal disease are ineligible

- Hormone receptor status:

- Not specified

PATIENT CHARACTERISTICS:

- ECOG (Eastern Cooperative Oncology Group) performance status 0-2

- Male or female

- Menopausal status not specified

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

- Platelet count ≥ 100,000/mm^3

- Creatinine clearance > 50 mL/min

- Fertile patients must use effective contraception

- No history of another severe and/or life-threatening medical disease

- No other active primary malignancy

- Not pregnant or nursing

- Negative pregnancy test

- Patients with asymptomatic HIV infection are eligible

- Liver dysfunction score ≤ 9

- No pre-existing liver disease (i.e., cirrhosis or active viral hepatitis)

- No active gastrointestinal malabsorption illness

- No clinically significant cardiac disease, including the following:

- Congestive heart failure, symptomatic coronary artery disease, and cardiac
arrhythmias not well controlled with medication, or myocardial infarction within
the past six months

- No prior unanticipated severe reaction to fluoropyrimidine therapy, known
hypersensitivity to fluorouracil, or known dihydropyrimidine dehydrogenase deficiency

- No history of uncontrolled seizures or central nervous system disorders

- No significant history of noncompliance to medical regimens

- No clinically significant psychiatric disability that would preclude study compliance

PRIOR CONCURRENT THERAPY:

- No previous capecitabine

- Up to 3 prior cytotoxic regimens allowed for metastatic disease

- Prior noncytotoxic therapy allowed (e.g., hormonal treatment or trastuzumab)

- No other concurrent therapies intended to treat the primary condition including
chemotherapy, biologic agents, or immunotherapy

- No concurrent anti-estrogen therapy, radiation therapy, or investigational systemic
therapy

- No other concurrent investigational drugs

- No concurrent use of the following drugs: warfarin for full anticoagulation,
cimetidine, or azidothymidine (AZT)

- Mini-dose warfarin for prophylaxis of central venous catheter thrombosis allowed

- At least 4 weeks since prior sorivudine or brivudine

- Concurrent use of bisphosphonates allowed if initiated before beginning study therapy

- Concurrent use of megestrol acetate suspension as an appetite stimulant allowed