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