DISEASE CHARACTERISTICS:

* Histologically or cytologically confirmed unresectable or metastatic gastrointestinal stromal tumor (GIST)

* Primary (gastrointestinal or intra-abdominal origin) tumor
* At least 1 measurable lesion by x-ray, CT, MRI, ultrasound, or physical examination

* If lesions within prior radiation port are used as target lesions for response assessment, those lesions must have demonstrated clear progression after completion of radiotherapy
* No uterine or retroperitoneal sarcomas or non-intra-abdominal leiomyosarcomas

PATIENT CHARACTERISTICS:

Age:

* Not specified

Performance status:

* Zubrod 0-2

Life expectancy:

* Not specified

Hematopoietic:

* WBC (white blood count) at least 3,000/mm\^3
* Platelet count at least 100,000/mm\^3

Hepatic:

* Bilirubin no greater than 2 times upper limit of normal (ULN)

Renal:

* Creatinine no greater than 1.5 times ULN

Other:

* Not pregnant or nursing
* Negative pregnancy test
* Fertile patients must use effective contraception
* No medical or psychological conditions that would preclude study participation
* No major infection requiring systemic antibiotics
* No uncontrolled bacterial, viral, or fungal infection
* No other prior malignancy within the past 5 years except:

* Adequately treated basal cell or squamous cell skin cancer
* Adequately treated stage I or II cancer in complete remission
* Carcinoma in situ of the cervix

PRIOR CONCURRENT THERAPY:

Biologic therapy:

* At least 30 days since prior biologic therapy
* Prior imatinib mesylate as adjuvant therapy or for metastatic disease allowed

Chemotherapy:

* No prior chemotherapy for GIST
* At least 30 days since other prior chemotherapy

Endocrine therapy:

* Not specified

Radiotherapy:

* See Disease Characteristics
* No prior radiotherapy for GIST
* No concurrent radiotherapy for GIST
* Concurrent palliative radiotherapy for painful metastases (encompassing a total portal of no greater than 5 x 5 cm) allowed

Surgery:

* See Disease Characteristics
* At least 4 weeks since prior major surgery and recovered

Other:

* At least 30 days since prior investigational drugs