Prognostic stratification of high-risk gastrointestinal stromal tumors in the era of targeted therapy

Background: Recently, a trial of adjuvant imatinib for primary RO-resected intermediate and high-risk gastrointestinal stromal tumors (GISTs) significantly improved recurrence-free survival. But identifying patients having higher chances of recurrence will reduce economic losses and prevent adverse side effects caused by adjuvant treatment. Methods: Tissue samples from 93 patients with high-risk GISTs were studied for p16, CD34, and CD44 protein expression and mutations of KIT and PDGFRA gene. Clinicopathologic, immunohistochemical, and mutation results were compared with clinical outcome by univariate and multivariate analyses. Results: KIT mutations were observed in 75 cases (81%) including 46 exon 11 deletion mutations and 31 deletions affecting codons 557-558. A novel 12 bp deletion mutation (KHNG484-488) on KIT exon 9 was detected in a small intestinal GIST. For recurrence-free survival, R0 resection, organ-confined disease stage, and female sex are better prognostic factors in univariate analysis and disease stage was the only factor predicting recurrence (P = 0.02) in multivariate analysis. In overall survival, mutation types, presence of mutation, location of GISTs, and mitosis were significant by univariate analysis. After multivariate analysis, mitotic counts and presence of KIT mutation corresponded to independent prognostic factors. Moreover, mitosis, KIT exon I I deletion mutation, and deletions affecting exon 557-558 predict recurrence in RO-resected high-risk GISTs (P < 0.05). Conclusion: Prognostic stratification in high-risk GISTs will help identify patients with high-risk GIST who may benefit from adjuvant therapy.