Imatinib Mesylate in Treating Patients With Recurrent Ewing's Family of Tumors or Desmoplastic Small Round-Cell Tumor

DISEASE CHARACTERISTICS: * Diagnosis of Ewing's family of tumors OR desmoplastic small round-cell tumor * Must have immunohistochemical evidence of expression of greater than 2+/4+ for either Kit (CD117) or platelet-derived growth factor receptor -a or -b * No symptomatic brain metastases * Asymptomatic brain metastases are allowed provided patient is not on concurrent anticonvulsants or corticosteroids PATIENT CHARACTERISTICS: Age * Over 16 Performance status * ECOG 0-2 Life expectancy * Not specified Hematopoietic * Absolute neutrophil count greater than 1,500/mm\^3 * Platelet count greater than 100,000/mm\^3 * Hemoglobin greater than 9 g/dL Hepatic * Bilirubin less than 1.5 times upper limit of normal (ULN) * SGOT and SGPT less than 2.5 times ULN * No chronic active hepatitis * No cirrhosis * No other acute or known chronic liver disease Renal * Creatinine less than 1.5 times ULN Cardiovascular * No concurrent poorly controlled or severe cardiovascular disease Pulmonary * No concurrent poorly controlled or severe pulmonary disease Other * HIV negative * No concurrent poorly controlled or severe central nervous system disease * No other concurrent poorly controlled or severe nonmalignant disease PRIOR CONCURRENT THERAPY: Biologic therapy * Not specified Chemotherapy * At least 3 weeks since prior chemotherapy Endocrine therapy * See Disease Characteristics Radiotherapy * At least 3 weeks since prior radiotherapy Surgery * More than 2 weeks since prior major surgery Other * More than 28 days since prior investigational agents