Interruption of imatinib in advanced gastrointestinal stromal tumor after prolonged imatinib maintenance in the absence of gross tumor lesions.

Abstract

11539 Background: Although current guidelines recommend indefinite imatinib treatment in advanced gastrointestinal stromal tumor (GIST) patients, prolonged imatinib treatment is often challenging. Imatinib-refractory progression-free survival (PFS) and overall survival were reportedly not different between those who interrupted imatinib and those did not. Methods: Clinical outcomes of 77 consecutive patients with recurrent or metastatic GIST who interrupted imatinib treatment after maintaining around 5 years of imatinib treatment in the absence of gross tumor lesions were retrospectively analyzed. Association between clinical factors and progression-free survival (PFS) following imatinib interruption was analyzed. Results: Median time from the absence of gross tumor lesions to imatinib interruption was 61.5 months (range 41.4–122.7 months). Since imatinib interruption, median PFS was 19.6 months, and the PFS rate at 60 months was 26.3%. Among patients who had progressive disease following interruption, imatinib re-introduction led to 88.6% objective response rate and 100% disease control rate, with the median imatinib-refractory PFS since re-introduction of 112.4 months. Complete removal of initial gross tumor lesion(s) (hazard ratio [HR] 0.32, 95% confidence interval [CI] 0.12–0.81, P = 0.016) and complete removal of residual gross tumor lesion(s) (HR 0.45, 95% CI 0.21–0.94, P = 0.033) by local treatment (vs. no local treatment or residual lesions after local treatment) were independently associated with favorable PFS. Conclusions: Interruption of imatinib may be considered with close surveillance in selected patients who maintained years of imatinib treatment in the absence of gross tumor lesions, especially for those who had complete removal of gross tumor lesions by local treatment.