This phase III study is evaluating whether receiving targeted therapy (imatinib) for three or five years is more effective in people with gastrointestinal stromal tumours following surgeryThree Versus Five Years of Adjuvant Imatinib as Treatment of Patients With Operable GIST With a High Risk for Recurrence: A Randomised Phase III Study

Exclusion

• Presence of distant metastases or local recurrence of GIST.
• Not willing to donate tumor tissue and/or blood samples for the study molecular studies.
• Presence of a substitution mutation at PDGFRA codon D842 (usually D842V).
• Administration of adjuvant imatinib longer than for 3 years is planned regardless of the result of randomization, or "life long" imatinib administration is planned.
• Prior adjuvant (+ neoadjuvant) therapy with imatinib mesylate for at least 35 months has not been completed, or the total duration of prior adjuvant (+ neoadjuvant) imatinib administration exceeds the total duration of 37 months.
• Neoadjuvant imatinib for a duration that exceeds 9 months.
• Longer than 4-week break during adjuvant imatinib administration.
• The dose of imatinib at completion of 3 years of adjuvant imatinib was 200 mg per day or less or greater than 800 mg per day.
• Patient has received any investigational anti-cancer agents during adjuvant imatinib or between completion of adjuvant imatinib and the date of randomization.
• Patient has been free of another malignancy for less than 5 years except if the other malignancy is not currently clinically significant nor requiring active intervention, or if the other malignancy is a basal cell skin cancer or a cervical carcinoma in situ. Recent existence of any other malignant disease is not allowed.
• Patient with Grade III/IV cardiac disease as defined by the New York Heart Association Criteria (i.e., congestive heart failure, myocardial infarction within 6 months of study entry).
• Female patients who are pregnant or breast-feeding.
• Severe and/or uncontrolled medical disease (i.e., uncontrolled diabetes, severe chronic renal disease, or active uncontrolled infection).
• Known diagnosis of human immunodeficiency virus (HIV) infection.
• Patient with a significant history of non-compliance to medical regimens or with inability to grant reliable informed consent.