RecruitingPhase 2Drug trialImatinib TDM in GISTImatinib can lead to long recurrence free survival in patients diagnosed with gastrointestinal stromal tumors (GIST); however side effects can significantly hinder quality of life for our patients. This study will use therapeutic drug monitoring to improve quality of life and symptoms and assess how many patients maintain therapeutic levels. Free drug levels and pharmokinetics of imatinib will also be monitored.