DISEASE CHARACTERISTICS: Histologically confirmed soft tissue sarcoma Malignant fibrous histiocytoma Liposarcoma Rhabdomyosarcoma Synovial sarcoma Malignant paraganglioma Fibrosarcoma Leiomyosarcoma Angiosarcoma Hemangiopericytoma Neurogenic sarcoma Unclassified sarcoma Miscellaneous sarcoma (including mixed mesodermal tumors of the uterus) Gastrointestinal stromal tumor (GIST) (must be c-kit positive) No malignant mesothelioma, chondrosarcoma, neuroblastoma, osteosarcoma, Ewing's sarcoma, or embryonal rhabdomyosarcoma Phase I study and nonGIST phase II study patients: Must have received one prior first line combination chemotherapy regimen or two first line single agent regimens Adjuvant chemotherapy not considered first line, unless disease progression within 6 months of treatment Phase II GIST patients: No more than one prior first line combination chemotherapy regimen or two first line single agent regimens Adjuvant chemotherapy not considered first line, unless disease progression within 6 months of treatment Measurable disease with evidence of progression in past 6 weeks Osseous lesions and pleural effusions not considered measurable No symptomatic or known CNS metastases