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 uncontro…