Inclusion Criteria

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 the past 5 years except basal cell skin cancer,
carcinoma in situ of the cervix, or a primary malignancy that is not currently
clinically significant and does not require active intervention

- No gastrointestinal obstruction or major bleeding episode requiring immediate
surgical intervention

- No uncontrolled diabetes

- No other severe or uncontrolled medical disease

- No significant history of noncompliance to medical regimens

PRIOR CONCURRENT THERAPY:

- No concurrent anticancer biologic agents

- More than 4 weeks since prior chemotherapy (6 weeks for nitrosourea or mitomycin)
unless disease is rapidly progressing

- No concurrent anticancer chemotherapy

- At least 28 days since prior radiotherapy

- More than 2 weeks since prior major surgery except tumor biopsy Other

- At least 28 days since prior investigational drugs

- At least 28 days since prior imatinib mesylate

- No concurrent therapeutic doses of warfarin

- Concurrent low-molecular weight heparin or mini-dose warfarin (1 mg per day)
prophylaxis is allowed