Background: Imatinib mesylate, a small-molecule tyrosine kinase inhibitor, is currently used for adjuvant therapy of patients who have undergone resection of high-risk gastrointestinal stromal tumors (GISTs). There are no data concerning the efficacy and safety of postoperative adjuvant therapy with imatinib for Japanese or East Asian patients with GIST. Methods: A single-arm, open-label, multicenter trial was conducted in 17 hospitals in Japan. The eligibility criteria included histologically proven primary high-risk GISTs with macroscopic complete resection. Patients were treated with imatinib at a dose of 400 mg/day for 1 year after surgery. The primary endpoint was recurrence-free survival as assessed by Kaplan-Meier analysis. The secondary endpoints were overall survival and safety. This study was registered with ClinicalTrials.gov, number NCT00171977. Results: A total of 64 patients were enrolled between September 2004 and July 2006. The median age of the patients was 59.5 years. Forty-nine (76.6%) patients completed the 1-year treatment, whereas 15 (23.4%) patients did not complete the treatment owing to recurrence, toxicities, and consent withdrawal. At the median follow-up period of 109 weeks, 20 patients had recurrence. The 3-year recurrence rate was 42.7% (95% confidence interval 29.2-56.3%), which exceeded the expected recurrence rate in this trial. The recurrence-free and overall survival rates at 2 years were 71.1 and 93.7%, respectively. The most frequent adverse drug reaction of any grade was eyelid edema (48.4%), followed by neutropenia (40.6%), leukopenia (39.1%), nausea (39.1%), rash (37.5%), and peripheral edema (37.5%), most of which were mild and manageable. Conclusions: Adjuvant therapy with imatinib at 400 mg/day for 1 year is well tolerated by Japanese patients and possibly reduces the risk of early recurrence of high-risk GISTs.
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