Inclusion Criteria

DISEASE CHARACTERISTICS: Metastatic breast cancer Bidimensionally measurable or evaluable
disease No bone metastases as only site of measurable or evaluable disease that has been
receiving bisphosphonate therapy for less than 2 months No known evidence of brain
metastases, lymphangitis lung metastases, or carcinomatous meningitis Hormone receptor
status: Not specified

PATIENT CHARACTERISTICS: Age: 18 and over Sex: Female Menopausal status: Not specified
Performance status: ECOG 0-1 Life expectancy: At least 3 months Hematopoietic: WBC at
least 3,000/mm3 Granulocyte count at least 1,500/mm3 Platelet count at least 100,000/mm3
Hepatic: Bilirubin no greater than 1.5 mg/dL AST or ALT no greater than 2.5 times upper
limit of normal (ULN) Renal: Creatinine no greater than 1.5 times ULN Calcium no greater
than 1.3 times ULN Other: Not pregnant or nursing Negative pregnancy test Fertile patients
must use effective contraception No history of other cancers except curatively treated
carcinoma in situ of the cervix or nonmelanomatous skin cancer No active serious infection
or other serious underlying medical condition that would preclude study therapy No
dementia or significantly altered mental status that would preclude study consent No known
hypersensitivity to fluorouracil-uracil or leucovorin calcium

PRIOR CONCURRENT THERAPY: Biologic therapy: No concurrent immunotherapy Concurrent colony
stimulating factors (e.g., filgrastim (G-CSF), sargramostim (GM-CSF)) allowed only during
time off treatment during each course Chemotherapy: No prior chemotherapy for metastatic
disease At least 6 months since prior adjuvant chemotherapy and recovered Prior adjuvant
fluorouracil allowed provided not infusional No prior fluorouracil-uracil with or without
leucovorin calcium, capecitabine, S-1, or ethynyl uracil No other concurrent chemotherapy
Endocrine therapy: Prior hormonal therapy for metastatic disease or in adjuvant setting
allowed Recovered from toxicity No concurrent hormonal anticancer therapy Radiotherapy:
Prior radiotherapy for metastatic disease or in adjuvant setting allowed At least 2 weeks
since prior radiotherapy and recovered No prior radiotherapy to greater than 30% of bone
marrow No concurrent radiotherapy except for palliation of painful bone metastases,
pathologic fractures of known lytic disease, or brain lesions that develop Surgery: Not
specified Other: No other concurrent investigational therapy No other concurrent
anticancer drugs No concurrent halogenated antiviral agents (e.g., lodenosine,
fialuridine, L-FMAU, emtricitabine, or sorivudine) No concurrent initiation of
bisphosphonate therapy for development of new bone lesions or progression of existing bone
lesions