A human monoclonal antibody directed against the human epidermal growth factor receptor ErbB3 (HER3), with potential antineoplastic activity. Upon administration, the anti-ErbB3 monoclonal antibody CDX-3379 targets and binds to a unique epitope on ErbB3, thereby preventing ErbB3 phosphorylation and both ligand-dependent and ligand-independent ErbB3 signaling. This inhibits cellular proliferation and survival of ErbB3-expressing tumor cells. ErbB3, a member of the epidermal growth factor receptor (EGFR) family of receptor tyrosine kinases, is frequently overexpressed in a variety of tumors and its overexpression generally correlates with poor prognosis and tumor resistance.