OBJECTIVES: * Determine the confirmed complete and partial response rate in women with progressive stage IV adenocarcinoma of the breast treated with imatinib mesylate and capecitabine. * Determine the 6-month progression-free survival of patients treated with this regimen. * Determine the toxicity of this regimen in these patients. * Correlate, preliminarily, c-kit and platelet-derived growth factor receptor expression with estrogen and progesterone receptor status, response, survival, and time to disease progression in patients treated with this regimen. OUTLINE: This is a multicenter study. Patients receive oral imatinib mesylate\* once daily on days 1-21 and oral capecitabine twice daily on days 1-14. Courses repeat every 21 days in the absence of disease progression or unacceptable toxicity. NOTE: \*If the patient tolerates the starting dose of imatinib mesylate in course 1, the dose will be increased in subsequent courses. Patients are followed every 6 months for 3 years. PROJECTED ACCRUAL: A total of 25-70 patients (25-45 patients with measurable disease and 25 with non-measurable disease) will be accrued for this study within 2 years.
* 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
is designated in this study