Recent preclinical study has suggested a potential possibility that imatinib might promote tumor growth in the presence of secondary resistance mutations [10]. This result imply that intermittent dosing schedule of imatinib rechallenge might be better than continuous dosing schedule in terms of controlling tumors harboring secondary resistance mutations. In addition, in these heavily pretreated patients, even mild grade of toxicity may significantly impair quality of life, and intermittent dosing schedule may have an advantage in this context. Therefore, investigators hypothesize that intermittent dosing schedule of imatinib rechallenge might be feasible and effective in patients with TKI-refractory GISTs. This study will assess the feasibility of intermittent imatinib dosing schedule in patients with GISTs who had failures from both imatinib and sunitinib.