DISEASE CHARACTERISTICS:

• Histologically and/or cytologically confirmed breast cancer
• Advanced and/or metastatic disease

• At least 1 measurable lesion

  • At least 20 mm by conventional techniques OR at least 10 mm by spiral CT scan
• No CNS metastases

• Hormone receptor status:

  • Not specified

PATIENT CHARACTERISTICS:

Age:

• 18 and over

Sex:

• Female

Menopausal status:

• Not specified

Performance status:

• Karnofsky 70-100%

Life expectancy:

• At least 12 weeks

Hematopoietic:

• Neutrophil count at least 1,500/mm^3
• Platelet count at least 100,000/mm^3

Hepatic:

• Bilirubin no greater than 1.25 times upper limit of normal (ULN)
• AST/ALT no greater than 2.5 times ULN (5 times ULN if liver metastases present)
• Alkaline phosphatase no greater than 2.5 times ULN (5 times ULN if liver metastases present OR 10 times ULN if bone metastases present)
• No hepatitis

Renal:

• Creatinine no greater than 1.5 times ULN
• Creatinine clearance at least 50 mL/min

Cardiovascular:

• No clinically significant cardiac disease
• No congestive heart failure
• No symptomatic coronary artery disease
• No cardiac arrhythmias poorly controlled with medication
• No myocardial infarction within the past 12 months even if adequately controlled with medication

Other:

• Not pregnant or nursing
• Negative pregnancy test
• Fertile patients must use effective contraception
• HIV negative
• No severe pain inadequately controlled by analgesics
• No prior severe and unexpected reaction to fluoropyrimidine therapy
• No known hypersensitivity to fluorouracil
• No impaired physical integrity of the upper gastrointestinal tract
• No malabsorption syndrome
• No inability to swallow tablets
• No history of uncontrolled seizures, central nervous system disorder, or psychiatric disability that would preclude study participation
• No serious uncontrolled infection

PRIOR CONCURRENT THERAPY:

Biologic therapy:

• Not specified

Chemotherapy:

• At least 2 but no more than 3 prior chemotherapy regimens
• At least 1 prior chemotherapy regimen containing paclitaxel and an anthracycline as adjuvant therapy or for advanced and/or metastatic disease

Endocrine therapy:

• Not specified

Radiotherapy:

• No prior radiotherapy to target lesions unless there is evidence of new disease within the irradiated field
• No concurrent radiotherapy

Surgery:

• No prior organ allografts

Other:

• At least 4 weeks since prior investigational drug
• No concurrent enrollment on other investigational study
• No other concurrent anticancer agents