Seribantumab (MM 121), a fully human IgG2 monoclonal antibody, specifically targets HER3, inhibiting the activation of the epidermal growth factor receptor (ErbB) family and its subsequent signaling. This action effectively blocks neuregulin 1 (NRG1) fusion-dependent tumorigenesis within in vitro and in vivo studies of patient-derived cancer models in breast, lung, and ovarian cancers [1].