Co-existence of positive MET FISH status with EGFR mutations signifies poor prognosis in lung adenocarcinoma patients

MET, a receptor tyrosine kinase for hepatocyte growth factor, is associated with tumor progression and acquired resistance to epidermal growth factor tyrosine kinase inhibitors (EGFR-TKI). Therefore, MET gene alterations could be both prognostic and predictive. Fluorescence in situ hybridization (FISH) is one method for assessing gene alteration, but the frequency of positive cases varies due to a lack of standardized criteria. We evaluated MET gene copy number in lung adenocarcinoma and its association with clinicopathological characteristics. FISH was applied to evaluate high MET gene copy number and true amplification in 138 lung adenocarcinoma patients using two criteria: the Cappuzzo scoring system and PathVysion. MET positive cases according to the Cappuzzo scoring system evidenced both aneuploidy and true amplification, whereas PathVysion revealed only amplification. Proportion of MET FISH positive cases was 15% and 4% determined by the Cappuzzo system and PathVysion, respectively. PathVysion demonstrated higher frequencies of MET FISH positives among men and smokers and evidenced no MET FISH positives in patients with bronchioloalveolar carcinoma. Prognosis was significantly associated with MET FISH positive only as defined by the PathVysion system (gene amplification), not by the Cappuzzo system. However, progression-free survival time of patients with both EGFR mutations and MET FISH positive defined by the Cappuzzo scoring system was significantly shorter than with EGFR mutations alone. These results suggest that MET FISH is a potential prognostic factor and coexistence of MET FISH with EGFR mutations signifies worse prognosis.