Prognostic significance of KIT exon 11 deletion mutation in intermediate-risk gastrointestinal stromal tumor

Aim: Benefit of adjuvant imatinib therapy following curative resection in patients with intermediate-risk gastrointestinal stromal tumor (GIST) is unclear. GIST-specific exon mutations, in particular exon 11 deletions, have been shown to be prognostic. We hypothesize that specific KIT mutations may improve risk stratification in patients with intermediate-risk GIST, identifying a subgroup of patients who may benefit from adjuvant therapy. Methods: In total, 142 GIST patients with complete clinicopathologic and mutational data from two sites were included. Risk classification was based on the modified National Institute of Health (NIH) criteria. Results: In this cohort, 74% (n = 105) of patients harbored a KIT mutation; 61% (n = 86) were found in exon 11 of which nearly 70% were KIT exon 11 deletions (n = 60). A total of 18% (n = 25) of cases were classified as having intermediate-risk disease. Univariate analysis confirmed tumor size, mitotic index, nongastric origin, presence of tumor rupture and modified NIH criteria were adversely prognostic for relapse-free survival (RFS). Among KIT/PDGFRA mutants, KIT exon 11 deletions had a significantly worse prognosis (hazard ratio 2.31; 95% confidence interval, 1.30–4.10; P = 0.003). Multivariate analysis confirmed KIT exon 11 deletion (P = 0.003) and clinical risk classification (P < 0.001) as independent adverse prognostic factors for RFS. Intermediate-risk patients harboring KIT exon 11 deletions had RFS outcomes similar to high-risk patients. Conclusion: The presence of KIT exon 11 deletion mutation in patients with intermediate-risk GIST is associated with an inferior clinical outcome with RFS similar to high-risk patients.