A humanized monovalent monoclonal antibody directed against the hepatocyte growth factor receptor (c-Met) with potential antineoplastic activity. Onartuzumab binds to the extracellular domain of c-Met, preventing the binding of its ligand, hepatocyte growth factor (HGF); the activation of the c-Met signaling pathway is thus inhibited, which may result in cell death in c-Met-expressing tumor cells. c-Met, a receptor tyrosine kinase, is overexpressed on the cell surfaces of a variety of cancer cell types and may play a key role in their proliferation, invasion and survival.