Imatinib Mesylate With or Without Surgery in Treating Patients With Metastatic Gastrointestinal Stromal Tumor That is Responding to Imatinib Mesylate

DISEASE CHARACTERISTICS: * Histologically confirmed gastrointestinal stromal tumor expressing CD117+ or with documented mutation of the KIT or PDGFRA gene * Metastatic disease (liver and/or abdominal cavity) * No extra-abdominal metastases * Measurable disease according to RECIST criteria * Achieved complete response, partial response, or stable disease without progression since the start of imatinib mesylate therapy, documented according to RECIST * Underwent 6-12 months of treatment with imatinib mesylate as a standard of care or within other clinical studies (surgery should be feasible before the end of the 12th month from imatinib mesylate onset) * Surgically resectable residual disease as assessed by CT scan and/or MRI within the past 14 days PATIENT CHARACTERISTICS: * WHO performance status 0-1 * ANC \> 1,500/mm\^3 * Platelet count \> 100,000/mm\^3 * Hemoglobin ≥ 9 g/dL * Creatinine \< 120 μmol/L * Albumin \> 25 g/L * Total bilirubin \< 2 times upper limit of normal (ULN) * AST and ALT \< 2.5 times ULN (\< 5 ULN in case of liver metastases) * Alkaline phosphatase \< 2.5 times ULN (\< 5 ULN in case of bone or liver metastases) * Negative pregnancy test within the past 14 days * Fertile patients must use effective contraception * No uncontrolled hypertension (diastolic BP \> 95 mm Hg and systolic BP \> 170 mm Hg) * No myocardial infarction, unstable, or uncontrolled cardiac disease within the past 6 months * No history of arterial thrombosis or deep vein thrombosis within the past year * No bleeding diathesis, coagulopathy, or major bleeding within the past 6 months * No severe and/or uncontrolled concurrent medical disease, including any of the following conditions: * Diabetes * Chronic renal disease * Liver disease, including chronic viral hepatitis judged at risk of reactivation * Active infection, including HIV infection * No prior malignancy (other than in situ cervical cancer, in situ melanoma, or basal cell or squamous cell cancer of the skin) unless treated with curative intent and without evidence of disease for at least 3 years * No psychological, familial, sociological, or geographical condition potentially hampering compliance with the study protocol and follow-up schedule PRIOR CONCURRENT THERAPY: * See Disease Characteristics * No prior adjuvant or neo-adjuvant imatinib mesylate or other tyrosine kinase inhibitor * No coumadin-type anticoagulant \> 2mg/day within the past 7 days * No major surgery within the past 28 days * No medication that interacts moderately or strongly with the CYP3A system within the past 14 days