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