DISEASE CHARACTERISTICS:

• Histologically confirmed gastrointestinal stromal tumor (GIST)
• Measurable disease by conventional scans (CT scan or MRI) within 2 weeks prior to study registration
• Positive PET/CT scan with [^18F]-fluorodeoxyglucose uptake of the target lesions within 2 weeks prior to study registration
• No signs or history of CNS metastases

PATIENT CHARACTERISTICS:

• WHO performance status 0-2
• Hemoglobin ≥ 90 g/L (transfusion allowed)
• Neutrophil count ≥ 1.5 x 10^9/L
• Platelet count ≥ 100 x 10^9/L
• Bilirubin ≤ 2 times upper limit of normal (ULN)
• Alkaline phosphatase ≤ 2.5 times ULN
• AST and/or ALT ≤ 2.5 times ULN
• Not pregnant or nursing
• Negative pregnancy test
• Fertile patients must use effective contraception during and for 12 months after completion of study therapy
• No other malignancy within the past 5 years except for adequately treated carcinoma in situ of the cervix or localized nonmelanoma skin cancer
• No hypocalcemia (i.e., serum calcium ≤ lower limit of normal)

• No clinically significant cardiovascular disease, including any of the following:

  • Uncontrolled hypertension
  • Congestive heart failure within the past 6 months
  • QTc > 450 msec or major conduction abnormality (unless a cardiac pacemaker is present)

• No concurrent medical condition (e.g., active autoimmune disease or uncontrolled diabetes) that would impair the ability of the patient to participate in the study (at the judgment of the investigator) or that may increase the risk of toxicity, including any of the following:

  • Pleural or pericardial effusion of any grade
  • Clinically significant coagulation or platelet function disorder (e.g., known von Willebrand's disease)
  • Infection requiring intravenous antibiotics
  • Ongoing significant gastrointestinal bleeding
  • Nausea, vomiting, or malabsorption syndrome that could interfere with ingestion or absorption of oral dasatinib
• No known hypersensitivity to study drug

PRIOR CONCURRENT THERAPY:

• No prior therapy for GIST, particularly tyrosine kinase inhibitors at any time
• More than 30 days since prior participation in a clinical trial

• At least 7 days since prior and no concurrent potent CYP3A4 inhibitors, including any of the following:

  • Itraconazole, ketoconazole, miconazole, and voriconazole
  • Amprenavir, atazanavir, fosamprenavir, indinavir, nelfinavir, and ritonavir
  • Ciprofloxacin, clarithromycin, diclofenac, doxycycline, enoxacin, imatinib mesylate, isoniazid, ketamine, nefazodone, nicardipine, propofol, quinidine, and telithromycin

• At least 7 days since prior and no concurrent medications known to prolong the QT interval, including any of the following:

  • Quinidine, procainamide, disopyramide, amiodarone, sotalol, ibutilide, and dofetilide
  • Erythromycin and clarithromycin
  • Chlorpromazine, haloperidol, mesoridazine, thioridazine, and pimozide
  • Cisapride, bepridil, droperidol, methadone, arsenic, chloroquine, domperidone, halofantrine, levomethadyl, pentamidine, sparfloxacin, and lidoflazine
• No concurrent IV bisphosphonates during the first 8 weeks of study treatment
• No other concurrent experimental drugs or anticancer therapy
• No concurrent drugs contraindicated for use with dasatinib, according to the dasatinib investigator's brochure