This study will evaluate efficacy and safety of nilotinib versus imatinib in adult patients with unresectable or metastatic gastrointestinal stromal tumors (GIST).

Inclusion Criteria:

1. Histologically confirmed diagnosis of GIST which is unresectable and/or metastatic and either:

   • have not received any prior anti-neoplastic therapy other than adjuvant imatinib. Note: newly diagnosed patients may have received up to 14 days of treatment with imatinib for disease management while awaiting entry to the study or
   • recurrent GIST after stopping adjuvant treatment with imatinib and no subsequent treatment with any other therapies.

2. At least one measurable site of disease on CT/MRI scan

3. Performance status ≤ 2 (capable of self-care but unable to carry out any work)

4. Normal organ, electrolyte and marrow function

Exclusion Criteria:

1. Any prior anti-neoplastic therapy with the exception of patients who have received adjuvant imatinib or patients with newly diagnosed metastatic/ unresectable GIST whose disease requires therapy while awaiting entry to the study.
2. Disease progression during adjuvant therapy with imatinib
3. History of active malignancy (other than GIST) within 10 years prior to study entry with the exception of previous or concomitant basal cell skin cancer, previous cervical carcinoma in situ.
4. Impaired cardiac function

Other protocol-defined inclusion/exclusion criteria may apply