Post-surgical imatinib had no impact on imatinib failure–free survival (IFFS) or overall survival in patients with high- or intermediate-risk gastrointestinal stromal tumor (GIST), but it did have an effect on relapse-free survival, according to a new study.
The introduction of tyrosine kinase inhibitors (TKIs) revolutionized the treatment of GISTs, but secondary resistance remains an issue. This randomized, open-label, multicenter phase III trial, which began in 2004, represents an early effort to test imatinib in the adjuvant setting.
The study included 908 patients, randomized to either imatinib 400 mg daily for 2 years following surgery (454 patients) or to observation (454 patients). Of those patients, 835 were eligible for this analysis; results were published in the Journal of Clinical Oncology.
After a median follow-up of 4.7 years, the 5-year IFFS was 87% in the imatinib patients and 84% in the observation patients, for a hazard ratio of 0.79 (98.5% confidence interval [CI], 0.50–1.25; P = .21). The relapse-free survival, though, was better with imatinib, at 84% at 3 years compared with 66%; at 5 years, the rates were 69% and 63% (log-rank P < .001).
Overall survival was not different between the imatinib and observation groups, at 100% and 99%, respectively. The 5-year IFFS among 528 patients deemed high-risk by a local pathologist was 79% with imatinib and 73% without. Among 336 patients deemed high-risk by a central review, these rates were 77% and 73%, respectively.
“Clearly, a crucial finding of adjuvant trials in GIST, including ours, has been that stopping adjuvant therapy is followed by relapse in at least most patients expected to experience relapse in the absence of any adjuvant therapy,” the authors wrote. “It follows that adjuvant imatinib therapy does not seem to cure minimum residual disease in patients with resected GIST.”
They concluded that this study confirms a relapse-free survival benefit with adjuvant imatinib in GIST, but observing any resulting benefit to overall survival will require substantially longer follow-up. “The issue of optimum adjuvant treatment duration remains a question for clinical research,” they wrote.