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 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