A monoclonal antibody against RON (recepteur d'origine nantais; macrophage stimulating 1 receptor), with potential antineoplastic activity. Narnatumab binds to RON, thereby preventing binding of its ligand hepatocyte growth factor-like protein (HGFL or macrophage-stimulating protein (MSP)). This may prevent RON receptor-mediated signaling and may prevent cellular proliferation in tumor cells overexpressing RON. RON, a receptor tyrosine kinase, is overexpressed in a variety of epithelial cancer cell types and plays an important role in cellular proliferation, migration and invasion.