Retrospective study of adjuvant imatinib versus observation after resection of gastrointestinal stromal tumors with KIT exon 9 mutations

Gastrintestinal stromal tumors (GISTs) harboring KIT exon 9 mutations represent a biologically distinct subgroup with reduced sensitivity to standard-dose imatinib in the advanced setting. The benefit of adjuvant imatinib in this population is not clear. A retrospective cohort study, conducted at 35 referral centers in Europe, the US, and Japan, evaluated adjuvant imatinib after resection of GISTs. Coprimary endpoints were recurrence-free survival (RFS) and overall survival (OS). The study included 367 patients (51% male, mean age 56 ± 13 years). Among these, 24.8% were observed and 75.2% received adjuvant imatinib (median duration 27.3 months; 42% treated ≥ 3 years). Adjuvant imatinib was associated with significantly longer RFS (HR 0.19; 95% CI 0.10-0.36) and OS (0.37; 0.17-0.83) in the full cohort. Similar results were obtained in the group with modified National Institutes of Health criteria high-risk disease. The authors conclude that adjuvant imatinib was associated with delayed recurrece and improved survival among patients with GISTs harboring KIT exon 9 mutations.