DISEASE CHARACTERISTICS:

• Histologically confirmed gastrointestinal stromal tumor (GIST)

  • Metastatic or unresectable disease
• Immunohistochemical confirmation of KIT (CD117) expression by tumor as documented by DAKO antibody staining

• Measurable or non-measurable disease by conventional imaging (CT scan or MRI) or physical examination

  • If a target lesion has been previously embolized or irradiated, there must be objective evidence of progression to be considered for response assessment
• No known brain metastasis

PATIENT CHARACTERISTICS:

• WHO performance status 0-3
• Bilirubin ≤ 1.5 times upper limit of normal (ULN)
• AST and ALT ≤ 2.5 times ULN (≤ 5 times ULN if hepatic metastases are present)
• Creatinine ≤ 1.5 times ULN
• ANC ≥ 1,000/mm³
• Platelet count ≥ 100,000/mm³
• Hemoglobin ≥ 9 g/dL (transfusions allowed)
• Not pregnant or nursing
• Negative pregnancy test
• Fertile patients must use effective barrier contraception during and for up to 3 months after completion of study therapy
• No NYHA class III-IV cardiac disease
• No congestive heart failure or myocardial infarction within the past 2 months
• No severe and/or uncontrolled concurrent medical disease (e.g., uncontrolled diabetes, uncontrolled chronic renal or liver disease, or active uncontrolled infection [e.g., HIV])
• No other prior malignancy except adequately treated basal cell or squamous cell skin cancer, carcinoma in situ of the cervix, adequately treated stage I or II cancer from which the patient is currently in complete remission, or any other cancer from which the patient has been disease-free for 5 years
• No medical, psychological, familial, sociological, or geographical condition that, in the opinion of the investigator, may preclude the patient's ability to tolerate or complete study treatment, comply with study protocol and follow-up schedule, or give reliable informed consent

PRIOR CONCURRENT THERAPY:

• Recovered from all prior therapy
• More than 28 days since prior chemotherapy, biologic therapy, or any other investigational drug
• More than 14 days since prior major surgery

• No concurrent therapeutic anticoagulation with coumarin derivatives

  • Concurrent therapeutic anticoagulation with low-molecular weight heparin allowed
  • Concurrent mini-dose coumarin derivatives (i.e., equivalent to 1 mg of oral warfarin daily) as prophylaxis allowed
• No concurrent cytokines (i.e., filgrastim [G-CSF] or sargramostim [GM-CSF]) to support blood counts
• No other concurrent investigational drugs
• No other concurrent anticancer agents, including chemotherapy, radiotherapy, or anticancer biologic therapy