S9926 Temozolomide in Patients With Unresectable/Metastatic Gastrointestinal Stromal Tumors

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