Perioperative Imatinib Mesylate in Treating Patients With Locally Advanced Gastrointestinal Stromal Tumor

Criteria: * DISEASE CHARACTERISTICS: * Histologically confirmed gastrointestinal stromal tumor * Locally advanced disease: tumour size \>5 cm and mitotic count \>5/HPF; tumour size \>10 cm; mitotic count \>10/HPF * Potentially resectable disease: Multivisceral resection may be necessary to get sufficient margins * Documented c-kit (CD117) expression by immunohistochemical analysis of either initial core specimen or, if recurrent disease, from original tumor block * At least 1 site of measurable disease * No known brain metastases * PATIENT CHARACTERISTICS: Age:18 and over Performance status:ECOG 0-3 Life expectancy:Not specified * Platelet count \> 100,000/mm3 * Absolute neutrophil count \> 1,500/mm3 Hepatic * AST and ALT \< 2.5 times upper limits of normal (ULN) (5 times ULN if hepatic metastases are present) * Bilirubin \< 1.5 times ULN * No chronic active hepatitis * No cirrhosis * No other chronic liver disease Renal * Creatinine \< 1.5 times ULN * No chronic renal disease Cardiovascular * No New York Heart Association class III-IV cardiac disease * No congestive heart failure * No myocardial infarction within the past 6 months Immunology * No active uncontrolled infection * No known HIV positivity Other * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective barrier contraception during and for 3 months after completion of study treatment * Must be medically fit to undergo surgery * No other primary malignancy within…