This study will evaluate the efficacy, safety, tolerability of imatinib in the neoadjuvant treatment (pre-operatory) of patients with GIST. It will also evaluate the potential of imatinib to convert a tumor from inoperable to operable.

Inclusion Criteria:

• patients with age between 18 and 80 years
• diagnosis of GIST not previously treated
• Patients will be included in the protocol regardless of operability; in the case of an operable tumor, patients are eligible if, in the opinion of the surgeon, resection would be suboptimal, disfiguring or functionally disabling (i.e. incomplete resection or other which cold compromise severely the quality of life or other GI function)

Exclusion criteria:

• presence of metastatic disease
• use of other antineoplastic treatment (chemotherapy, immunotherapy, radiotherapy)

Other protocol-defined inclusion/exclusion criteria may apply.