S0338, Imatinib Mesylate and Capecitabine in Treating Women With Progressive Stage IV Breast Cancer

* Histologically or cytologically confirmed adenocarcinoma of the breast * Stage IV measurable disease * Disease progression after at least 1, but no more than 2, prior chemotherapy regimens for metastatic disease * Patients with hormone-sensitive tumors must have received prior hormonal therapy * Patients with human epidermal growth factor receptor 2 (HER2)/neu-overexpressing tumors (3+ by immunohistochemistry or amplified by fluorescent in situ hybridization) should have received trastuzumab (Herceptin®) in the adjuvant or metastatic setting (unless contraindicated) * No clinical evidence of or known brain or central nervous system (CNS) disease * Hormone Receptor status known * Female age 18 and over * Performance status Zubrod 0-2 * Absolute neutrophil count \> 1,500/mm\^3 * Leukocyte count \> 3,000/mm\^3 * Platelet count \> 100,000/mm\^3 * Bilirubin normal * aspartate aminotransferase (AST) / alanine aminotransferase (ALT) \< 2.5 times upper limit of normal * Creatinine normal OR Creatinine clearance \> 60 mL/min * Not pregnant or nursing * Fertile patients must use effective contraception during and for 3 months after study participation * No history of severe hypersensitivity reaction to compounds of similar chemical or biological composition to imatinib mesylate, capecitabine, or fluorouracil * 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 * No prior biologic therapy (e.g., vaccines) * No concurrent filgrastim (G-CSF) for chemotherapy-induced neutropenia * No prior capecitabine or fluorouracil for metastatic breast cancer * Prior hormonal therapy allowed * More than 4 weeks since prior radiotherapy - Previously irradiated area(s) must not be the only site of disease * More than 4 weeks since prior major surgery * More than 4 weeks since prior therapy for breast cancer * No concurrent combination antiretroviral therapy for HIV-positive patients * No other concurrent investigational or commercial agents or therapies for metastatic breast cancer