- Failed prior therapy with imatinib followed by sunitinib for the treatment of unresectable or metastatic GIST. Note the following specific criteria for the two parts of the trial: • Dose-escalation part: patients who failed prior therapy with imatinib and then have failed therapy with sunitinib. Treatment failure may be due to either disease progression on therapy (both imatinib and sunitinib) or intolerance to therapy (sunitinib) • Dose-escalation part patients may have had additional lines of therapy than imatinib and sunitinib dose-expansion part: patients must have documented disease progression on both imatinib and sunitinib. In addition, patients may have had no more than two lines of prior therapy (i.e. treatment with imatinib followed by treatment with sunitinib). • Note: Adjuvant imatinib will not count as a prior course of imatinib for the purposes of this criterion 6. Radiological (CT/MRI) confirmation of disease progression (RECIST criteria) during prior therapy with imatinib and sunitinib will be required for patients entering the Dose-expansion part