 However, resistance to imatinib may develop and represents a further clinical challenge. Sunitinib has recently been approved by the FDA for patients whose disease has progressed or who are intolerant to imatinib therapy. Patients with tumor progressing on sunitinib or another 2nd line agent have limited therapeutic alternatives. Reinstitution of imatinib, if possible, is considered an acceptable option for these patients because it may slow the rate of disease progression even in the setting of prior imatinib failure; however a more optimal 3rd line treatment is needed. AMN107 is a novel aminopyrimidine, available as an oral formulation that is ATP -competitive inhibitor of BCR-ABL,more potent than Imatinib. It inhibits proliferation and autophosphorylation of 32 out of 33 BCR-ABL point mutations. In addition AMN107 also inhibits PDGFRα,PDGFRβ, and KIT. Preliminary data from an ongoing Phase I study in imatinib-resistant GIST patients CAMN107A2103 indicate that AMN107 alone 400 mg BID and in combination with imatinib imatinib 400 mg BID plus AMN107 200 mg QD and 400 mg QD is well tolerated in this pre-treated patients. 