A fully human monoclonal antibody directed against the membrane-bound receptor HER3 (ERBB3) with potential antineoplastic activity. Patritumab binds to and inhibits HER3 activation, which may result in inhibition of HER3-dependent PI3K/Akt signaling and so inhibition of cellular proliferation and differentiation. HER3, a member of the epidermal growth factor receptor (EGFR) family of receptor tyrosine kinases, is frequently overexpressed in solid tumors, including breast, lung, and colorectal tumors of epithelial origin; it has no active kinase domain itself but is activated through heterodimerization with other members of the EGFR receptor family that do.