Inclusion Criteria:

• Patients >= 18 years of age
• Histologically documented diagnosis of GIST which is malignant as well as unresectable (=not amenable to surgery with curative intent) and/or metastatic and therefore incurable Immunohistochemical documentation of c-kit (CD117) expression by tumor
• At least one measurable site of disease (as defined by Southwestern Oncology Group Solid Tumor Response Criteria) which has not been previously embolised or irradiated
• Performance status 0,1, 2 or 3 (ECOG)
• Adequate end organ function, defined as the following: total bilirubin < 1.5 x ULN, SGOT and SGPT < 2.5 x UNL (or < 5 x ULN if hepatic metastases are present), creatinine < 1.5 x ULN, ANC > 1.5 x 109/L, platelets > 100 x 109/L
• Female patients of child-bearing potential must have negative pregnancy test within 7 days before initiation of study drug dosing. Post menopausal women must be amenorrheic for at least 12 months to be considered of non-childbearing potential. Male and female patients of reproductive potential must agree to employ an effective barrier method of birth control throughout the study and for up to 3 months following discontinuation of study drug
• Life expectancy of at least 6 months
• Written, voluntary, informed consent
• Patients who were previously treated with chemotherapy will be eligible for this study
• Patient who are at least 5 years free of melanoma will be eligible for this study

Exclusion Criteria:

• Patient has received any other investigational agents within 28 days of first day of study drug dosing
• Patient is < 5 years free of another primary malignancy except: if the other primary malignancy is not currently clinically significant nor requiring active intervention and CECOGs' approval is obtained, or if other primary malignancy is a basal cell skin cancer or a cervical carcinoma in situ. Existence of any other malignant disease is not allowed
• Patient with Grade III/IV cardiac problems as defined by the New York Heart Association Criteria. (i.e., congestive heart failure, myocardial infarction within 6 months of study)
• Female patients who are pregnant or breast-feeding.
• Patient has a severe and/or uncontrolled medical disease (i.e., uncontrolled diabetes, chronic renal disease, or active uncontrolled infection)
• Patient has a known brain metastasis
• Patient has an acute or known chronic liver disease (i.e., chronic active hepatitis, cirrhosis)
• Patient has a known diagnosis of human immunodeficiency virus (HIV) infection
• Patient received chemotherapy within 4 weeks (6 weeks for nitrosoureas or mitomycin-C) prior to study entry
• Patient previously received radiotherapy to >= 25 % of the bone marrow
• Patient had a major surgery within 2 weeks prior to study entry
• Patient with any significant history of non-compliance to medical regimens or with inability to grant reliable informed consent
• Therapeutic anticoagulation with warfarin (e.g. Coumadin® or Coumadine®)