An open-label, non-comparative study conducted to investigate the activity and safety of imatinib mesylate in refractory desmoplastic small round cell tumors expressing PDGF-R. Patients will be treated up to 12 months, or to disease progression. Tumor will be evaluated according to Recist criteria

Inclusion criteria:

1. Patients > 16 years of age.
2. Histologically documented diagnosis of DSRCT, unresponsive or in no complete remission after any conventional multimodality approach.
3. Immunohistochemical documentation of activated PDGF-R expression by tumor
4. At least one measurable site of disease
5. Performance status 0,1, 2 or 3 (Eastern Cooperative Oncology Group)
6. Adequate end organ function

Exclusion criteria:

1. Patient has received any other investigational agents within 28 days of first day of study drug dosing, unless the disease is rapidly progressing.
2. Patient is < 5 years free of another primary malignancy
3. Patient with congestive heart failure or myocardial infarction within 6 months of study
4. Female patients who are pregnant or breast-feeding.
5. Severe and/or uncontrolled medical disease
6. Known brain metastasis.
7. Chronic active hepatitis or cirrhosis
8. Known diagnosis of human immunodeficiency virus (HIV) infection.
9. Chemotherapy within 4 weeks prior to study entry, unless the disease is rapidly progressing.
10. Previous radiotherapy to > 25 % of the bone marrow
11. Major surgery within 2 weeks prior to study entry.

Other protocol defined inclusion/exclusion criteria may apply.