AXL and lung carcinoma: Although the role of AXL–GAS6 expression and signaling effects in lung cancer have been reported in recent years (Ishikawa et al. 2013; Shieh et al. 2005; Wimmel et al. 2001; Zhang et al. 2012), the role of AXL–GAS6 in brain metastases from lung cancer and its potential prognostic importance have not been well clarified.