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