Prognosis and predictive value of KIT exon 11 deletion in GISTs

BACKGROUND: KIT exon 11 mutations are observed in 60% of gastrointestinal stromal tumours (GIST). Exon 11 codes for residues Tyr568 and Tyr570, which play a major role in signal transduction and degradation of KIT. Our aim was to compare the outcome of patients with deletion of both Tyr568–570 (delTyr) and the most frequent deletion delWK557–558 (delWK). METHODS: Pathology and clinical characteristics of 68 patients with delTyr (n=26) or delWK (n=42) were reviewed and compared. RESULTS: GISTs with delTyr were more frequently extragastric than those with delWK (69 vs 26%, P<0.0005). After curative surgery, median relapse-free survival were 10.8 and 11.1 months for patients with delTyr (n=14) and delWK (n=29), respectively (P=0.92). All patients treated with imatinib for a non-resectable or metastatic GIST had an objective response (n=15) or a stable disease (n=21) as best response, regardless of mutation. Median progression-free survival with imatinib were 21.9 and 18.9 months for patients with GIST with delTyr (n=14) and delWK (n=22), respectively (P=0.43). CONCLUSION: In this large retrospective series, the type of KIT exon 11 mutation was correlated with the origin of GIST, but not with prognosis or response to imatinib.