Inclusion Criteria:

• Histological diagnosis of DT or CDS.
• Biomolecular or immunohistochemical evidence of Imatinib mesylate target (KIT, PDGFRα PDGFRβ activation and/or presence of PDGFα or PDGFβ)
• Measurable or evaluable disease
• Surgical resection of local disease unfeasible radically (or unaccepted by the patient, or amenable to become less demolitive, or easier, or likely more feasible, after cytoreduction) and/or metastatic disease.
• ECOG Performance status 0, 1, 2 or 3
• Adequate bone marrow, liver and renal function
• Female patients of child-bearing potential must have negative pregnancy test.
• Male and female patients of reproductive potential must agree to employ an effective method of birth control throughout the study.
• Written, voluntary, informed consent.

Exclusion Criteria:

• Previous treatment with any other investigational or not investigational agents within 28 days of first day of study drug dosing
• Other primary malignancy with <5 years clinically assessed disease-free interval, except basal cell skin cancer or cervical carcinoma in situ.
• Grade III/IV cardiac problems as defined by the New York Heart Association Criteria
• Severe and/or uncontrolled medical disease (i.e., uncontrolled diabetes, chronic renal disease, or active uncontrolled infection)
• Known brain metastasis.
• Known chronic liver disease (i.e., chronic active hepatitis, and cirrhosis).
• Known diagnosis of human immunodeficiency virus (HIV) infection.
• Previous radiotherapy to >/=25% of the bone marrow or within the previous 2 months on target lesion.
• Major surgery within 2 weeks prior to study entry.
• Expected non-compliance to medical regimens (e.g. psychiatric diseases).