MST1R and neoplasm: Crizotinib is a potent ALK, MET, ROS1, and RON inhibitor (Pfizer Inc., data on file).1,2 HGF, the only known ligand for MET, is involved in embryonic development, tissue regeneration, and tumor progression.25 In the kidney, HGF is expressed in mesangial and interstitial stromal cells, which are mesenchymal, while MET is expressed in nonmesenchymal cells, such as those of the tubular epithelium.