DISEASE CHARACTERISTICS:

• Histologically or cytologically confirmed stage IV breast cancer

  • Metastatic disease (M1) OR multiple sites of new disease that is clinically obvious metastatic disease (i.e., multiple sites of new osseous disease)

• Meets 1 of the following criteria:

  • Measurable disease

  • Non-measurable disease

    • MUC-1 antigen level > 2 times upper limit of normal AND level has increased by 1.5 times

• Must have documented MUC-1 antigen level

  • Either cancer antigen (CA) 15-3 or CA 27-29 allowed
• Must have received at least 1 prior hormonal therapy for metastatic disease (estogen receptor-positive patients only)

• No symptomatic brain or CNS metastases

  • Previously treated brain or CNS metastasis allowed provided radiotherapy was completed ≥ 8 weeks before study entry

• Hormone receptor status:

  • Not specified

PATIENT CHARACTERISTICS:

Age

• 18 and over

Sex

• Female

Menopausal status

• Not specified

Performance status

• Zubrod 0-2

Life expectancy

• Not specified

Hematopoietic

• No known existing uncontrolled coagulopathy

Hepatic

• Not specified

Renal

• Creatinine clearance > 40 mL/min

Cardiovascular

• No congestive heart failure
• No symptomatic coronary artery disease
• No cardiac arrhythmia not well controlled with medication
• No myocardial infarction within the past 12 months
• No other clinically significant cardiac disease

Gastrointestinal

• Able to take oral medication
• No uncontrolled nausea, vomiting, or diarrhea
• No lack of physical integrity of the upper gastrointestinal tract
• No malabsorption syndrome

Other

• Not pregnant or nursing
• Fertile patients must use effective contraception
• No active infection requiring systemic therapy
• No prior severe reaction to fluoropyrimidines
• No known sensitivity to fluorouracil
• No known dihydropyrimidine dehydrogenase deficiency
• No other malignancy within the past 5 years except adequately treated basal cell or squamous cell skin cancer or carcinoma in situ of the cervix

PRIOR CONCURRENT THERAPY:

Biologic therapy

• No concurrent immunotherapy or biologic therapy for breast cancer
• No concurrent gene therapy for breast cancer
• No concurrent filgrastim (G-CSF)

Chemotherapy

• At least 14 days since prior chemotherapy and recovered
• No more than 2 prior chemotherapy regimens for metastatic disease
• No prior capecitabine for metastatic disease

• No prior oral cyclophosphamide for metastatic disease

  • Prior IV cyclophosphamide allowed
• No other concurrent chemotherapy for breast cancer

Endocrine therapy

• See Disease Characteristics
• No concurrent hormonal therapy for breast cancer

Radiotherapy

• See Disease Characteristics
• At least 14 days since prior radiotherapy to non-CNS disease sites and recovered
• No concurrent radiotherapy for breast cancer

Surgery

• Not specified

Other

• Concurrent bisphosphonates allowed

• No concurrent full-dose warfarin

  • Concurrent prophylactic warfarin (≤ 1 mg/day) to maintain port patency allowed
• No other concurrent antineoplastic therapy for breast cancer