Higher Expression of Receptor Tyrosine Kinase Axl, and Differential Expression of its Ligand, Gas6, Predict Poor Survival in Lung Adenocarcinoma Patients

BACKGROUND: Downstream activation through receptor tyrosine kinases (RTKs) plays important roles in carcinogenesis. In this study, we assessed the clinical involvement of Axl, an RTK, and its ligand, Gas6, in surgically treated lung adenocarcinoma. METHODS: Axl and Gas6 mRNA and protein expression levels were quantified using quantitative real-time polymerase chain reaction and immunohistochemistry, respectively, in completely resected lung adenocarcinoma tissues (n = 88) and were evaluated for correlation with clinicopathologic features and patient survival. RESULTS: Higher expressions of Axl mRNA/protein and Gas6 protein were significantly related to worse clinicopathological features and prognosis (5-year overall survival rates: Axl mRNA low: 72.3 %, high: 49.7 %, P = 0.047; Axl protein low: 77.5 %, high: 38.6 %, P < 0.001; and Gas6 protein low: 70.5 %, high: 48 %, P = 0.042). On the contrary, higher Gas6 mRNA expression was related to better clinicopathological features and prognosis (5-year overall survival rates: Gas6 mRNA low: 59.2 %, high: 81.8 %, P = 0.054). Multivariate analysis suggests that high Axl mRNA expression may be an independent factor for poor patient prognosis (P = 0.04). CONCLUSIONS: In lung adenocarcinoma, Axl and Gas6 expression levels were associated with tumor advancement and patient survival, thus rendering them as reliable biomarkers and potential targets for treatment of lung adenocarcinoma.