Three Versus Five Years of Adjuvant Imatinib as Treatment of Patients With Operable GIST

In this study, patients who have been diagnosed with gastrointestinal stromal tumor (GIST) and have been treated with adjuvant imatinib for 3 years after surgery will be randomly allocated in a 1:1 ratio to receive imatinib (Gleevec) for 2 more years (Arm A) or to stop imatinib (Arm B). The study participants are required to have histologically verified GIST with a high risk of GIST recurrence despite removal of all macroscopic GIST tissue at surgery and 3 years of adjuvant imatinib. The high risk of GIST recurrence is defined as one of the following: gastric GIST with mitotic count \>10/50 high power fields (HPFs) of the microscope, non-gastric GIST with mitotic count \>5/50 HPFs, or tumor rupture. Study participants allocated to Arm A will receive imatinib 400 mg/day for 24 months after the date of randomization. All study participants will be followed up using blood tests and computerized tomography (or MRI) of the abdomen. The computerized tomography examinations will be performed at 6 month intervals. A total of 300 patients will be entered to the study. The study hypothesis is that adjuvant imatinib given for a total of 5 years may prevent some of the GISTs to recur as compared to patients who receive adjuvant imatinib for 3 years, and there may be a difference in the rate of GIST recurrence between the two groups.