Background and Objectives Any gastrointestinal stromal tumors (GISTs) larger than 10 cm are classified as "high risk" according to the modified National Institutes of Health consensus criteria. We conducted a multicenter study to identify a subgroup with moderate prognosis even within the "high-risk" group. Methods We retrospectively collected data on 107 patients with tumors ≥10 cm from a multicenter database of GIST patients. Patients with macroscopic residual lesions or tumor rupture were excluded. The relationship between recurrence-free survival (RFS) and clinicopathological factors was analyzed. Results The median tumor size and mitotic count were 12.5 cm and 8/50 HPF. The RFS rate was 58.5% at 3 years, 52.1% at 5 years. Only mitotic count was an independent prognostic factor of RFS in the multivariate analysis (P = 0.001). The hazard ratio for recurrence in the subgroup with mitotic count >5/50 HPF was 2.91 (95% confidence interval, 1.53 to 5.56). The subgroup with mitotic count ≤5/50 HPF showed significantly better RFS than the mitotic count >5/50 HPF subgroup (P < 0.001). Conclusions Mitotic count is closely associated with outcome in patients with large GISTs. This suggests that the subset of large GISTs with low mitotic counts may be considered as "intermediate-risk" lesions. J. Surg. Oncol. 2014 109:67-70.
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