Inclusion Criteria

DISEASE CHARACTERISTICS:

- Histologically or cytologically confirmed invasive adenocarcinoma of the breast,
meeting 1 of the following high-risk criteria:

- T3 or T4 primary tumor

- 4 or more involved axillary lymph nodes (N2 nodal stage)

- Completed surgical excision

- No immediate reconstruction with autologous flap reconstruction

- Patients having tissue expanders or implants placed prior to radiation may
be enrolled at the physician's discretion

- No residual breast cancer

- Microscopically positive margins are allowed if a re-excision is not felt to be
clinically justified

- Candidate for radiotherapy

- Must not require bilateral radiotherapy

- No metastatic (stage IV) breast cancer by AJCC staging criteria

- Hormone receptor status not specified

- No CNS disorders

PATIENT CHARACTERISTICS:

- Life expectancy ≥ 6 months

- Karnofsky performance status 70-100%

- Menopausal status not specified

- Ambulatory

- Hemoglobin > 9 g/dL

- Platelet count > 100,000/mm³

- ANC > 1,500/mm³

- Serum AST, ALT, and alkaline phosphatase ≤ 2 times upper limit of normal (ULN)

- Total bilirubin normal

- Creatinine clearance > 50 mL/min

- Negative pregnancy test

- Not pregnant or nursing

- Fertile patients must use effective contraception during study and for 30 days after
the last study drug administration

- No serious, uncontrolled, concurrent infection(s)

- No diabetes with current or history of delayed wound healing or skin ulcers

- No autoimmune connective tissue disorder

- No prior unanticipated severe reaction to fluoropyrimidine therapy, known sensitivity
to 5-fluorouracil, or known dihydropyrimidine dehydrogenase (DPD) deficiency

- No other carcinomas within the last five years except cured non-melanoma skin cancer
and in-situ cervical cancer

- No clinically significant cardiac disease (e.g., congestive heart failure,
symptomatic coronary artery disease, or cardiac arrhythmias not well controlled with
medication) or myocardial infarction within the last 12 months

- No other serious uncontrolled medical conditions that the investigator feels might
compromise study participation, including any of the following:

- Uncontrolled seizures

- Psychiatric disability judged by the investigator to be clinically significant

- Physically intact upper gastrointestinal tract

- No malabsorption syndrome

- No uncompensated coagulopathy

- No patients whose breast size or body contour puts them at increased risk for skin
desquamation from standard radiotherapy

- Able to read and speak English

PRIOR CONCURRENT THERAPY:

- Fully recovered from surgery and chemotherapy with completely healed surgical wounds

- At least 4 weeks since completion of prior chemotherapy regimen, excluding
trastuzumab (Herceptin®)

- Concurrent trastuzumab allowed at the physician's discretion

- More than 4 weeks since prior participation in any investigational drug study

- At least 4 weeks since prior and no concurrent sorivudine or brivudine

- More than 2 weeks since prior major surgery

- No prior capecitabine

- No prior radiotherapy to the chest or ipsilateral lymphatics

- No concurrent hormonal therapy during course of chemotherapy or radiation therapy

- No concurrent allopurinol or cimetidine

- Concurrent coumadin is allowed