Gemcitabine +/- Imatinib Mesylate, Patients w/Previously Treated Metastatic Breast Cancer

DISEASE CHARACTERISTICS: * Histologically confirmed breast cancer * Locally advanced or metastatic disease * Disease progression after at least 1 prior chemotherapy regimen for metastatic disease * No more than 2 prior chemotherapy regimens for metastatic disease (prior neoadjuvant or adjuvant treatment will not be included in determining the number of prior chemotherapy regimens) * Measurable disease * No known symptomatic or untreated brain metastases or carcinomatous meningitis * Previously treated and clinically stable brain metastases allowed provided patient has been off steroids for \> 7 days * Hormone receptor status not specified PATIENT CHARACTERISTICS: * Male or female * Menopausal status not specified * ECOG performance status 0-2 * Life expectancy ≥ 3 months * Absolute neutrophil count ≥ 1,500/mm\^3 * Platelet count ≥ 100,000/mm\^3 * Bilirubin ≤ 1.5 times upper limit of normal (ULN) * AST or ALT ≤ 2.5 times ULN * Creatinine ≤ 1.5 times ULN OR creatinine clearance ≥ 60 mL/min * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective contraception during and for 3 months after completion of study therapy * Able to swallow oral medication * No coexisting medical condition that would preclude study compliance * No uncontrolled illness, including any of the following: * Symptomatic congestive heart failure * Unstable angina pectoris * Cardiac arrhythmia requiring therapy * Myocardial infarction within the past 6 months * Active infection * No New York Heart Association class III-IV cardiac disease * No history of allergic reaction attributed to compounds of similar chemical or biologic composition to gemcitabine hydrochloride and/or imatinib mesylate * No other primary malignancies within the past 5 years except for carcinoma in situ of the cervix or nonmelanoma skin cancer * No known chronic liver disease (i.e., chronic active hepatitis or cirrhosis) * No known HIV infection PRIOR CONCURRENT THERAPY: * See Disease Characteristics * Recovered from all prior therapy * More than 2 weeks since prior surgery * At least 2 weeks since prior hormonal therapy * At least 2 weeks since prior trastuzumab (Herceptin®) * At least 3 weeks since prior chemotherapy (6 weeks for nitrosoureas) * At least 3 weeks since prior anti-vascular endothelial growth factor therapy * More than 28 days since prior investigational agents * At least 3 weeks since prior radiotherapy * Must have evidence of ≥ 1 measurable target lesion outside the irradiated fields OR radiologically confirmed disease progression within the irradiated fields after completion of radiotherapy * No prior imatinib mesylate for metastatic disease * No prior gemcitabine hydrochloride for metastatic disease * More than 6 months since prior adjuvant gemcitabine hydrochloride * No other concurrent investigational or commercial agents * No concurrent therapeutic anticoagulation with warfarin (e.g., Coumadin® or Coumadine®) * Concurrent heparin or low-molecular weight heparin (e.g., Lovenox®) for therapeutic anticoagulation allowed * Concurrent prophylactic warfarin therapy (e.g., mini-dose Coumadin® ≤ 1 mg daily) to maintain catheter patency allowed * No concurrent routine chronic systemic corticosteroids * No concurrent medications that would preclude study compliance