AXL and esophageal squamous cell carcinoma: Reactivation of MAPK or cyclin/cdk deregulation [13], epithelial-to-mesenchymal transition (EMT), SRC activation [12] and upregulation of other RTKs (AXL [13], FGFR [22], or c-MET [23] have all been implicated in resistance in ESCC, but there is no clear indication of which is the optimal target in the largest proportion of ESCC patients.