Imatinib Mesylate in Treating Patients With Locally Advanced or Metastatic Dermatofibrosarcoma Protuberans or Giant Cell Fibroblastoma

DISEASE CHARACTERISTICS: * Histologically confirmed dermatofibrosarcoma protuberans or giant cell fibroblastoma * Locally advanced or metastatic disease * Measurable disease * Not amenable to surgery, radiotherapy, or combined modality therapy with curative intent * Documented progressive disease within the past 3 months * Previously irradiated lesions must show disease progression * Tumor expressing COL1A1/PDGF-beta by fluorescence in situ hybridization * Translocation t(17;22)(q22;q13) * No prior chemotherapy OR previously treated with 1, and only 1, line of combination chemotherapy with ifosfamide and doxorubicin OR 2 lines of single-agent therapy OR relapsed within 6 months after adjuvant chemotherapy PATIENT CHARACTERISTICS: Age * 18 and over Performance status * WHO 0-2 Life expectancy * Not specified Hematopoietic * Absolute neutrophil count ≥ 2,000/mm\^3 * Platelet count ≥ 100,000/mm\^3 * Hemoglobin ≥ 9 mg/dL\* NOTE: \*Transfusion allowed Hepatic * SGOT or SGPT ≤ 2.5 times upper limit of normal (ULN) (5 times ULN if hepatic metastases are present) * Bilirubin ≤ 1.5 times ULN * No uncontrolled hepatic disease Renal * Creatinine ≤ 1.5 times ULN * No uncontrolled renal disease Other * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective contraception during and for 3 months after study participation * HIV negative * No uncontrolled diabetes * No active or uncontrolled infection * No concurrent severe or uncontrolled medical disease * No medical, psychological, familial, sociological, or geographical condition that would preclude study participation, compliance, or giving informed consent * No other malignancy within the past 5 years except adequately treated basal cell or squamous cell skin cancer, carcinoma in situ of the cervix, or adequately treated stage I or II cancer currently in complete remission PRIOR CONCURRENT THERAPY: Biologic therapy * More than 28 days since prior biologic therapy * No concurrent filgrastim (G-CSF) or sargramostim (GM-CSF) * No concurrent anticancer biologic agents Chemotherapy * See Disease Characteristics * More than 28 days since prior chemotherapy * No concurrent chemotherapy Endocrine therapy * Not specified Radiotherapy * See Disease Characteristics * At least 6 months since prior radiotherapy * No concurrent radiotherapy * Concurrent palliative radiotherapy allowed provided radiotherapy will not be administered to a target lesion Surgery * Not specified Other * More than 28 days since prior investigational drugs * No concurrent therapeutic anticoagulation therapy with warfarin * Concurrent low-molecular weight heparin or mini-dose warfarin for prophylaxis of central venous catheter thrombosis allowed * No other concurrent anticancer agents * No other concurrent investigational drugs * No other concurrent cytostatic agents * No other concurrent tyrosine kinase inhibitors