Capecitabine and Radiation Therapy in Treating Patients With Nonmetastatic Breast Cancer After Surgery

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