Fepixnebart is an investigational, humanized immunoglobulin G4 (IgG4) monoclonal antibody being developed for the treatment of solid tumors. It functions as a dual-targeting ligand trap, specifically designed to bind with high affinity to two key ligands of the epidermal growth factor receptor (EGFR) pathway: epiregulin (EREG) and transforming growth factor-alpha (TGFα). By neutralizing these ligands in the tumor microenvironment, fepixnebart prevents them from binding to and activating EGFR, thereby inhibiting the downstream oncogenic signaling cascades (such as RAS/MAPK and PI3K/AKT pathways) that drive tumor cell proliferation, survival, and metastasis. The IgG4 isotype is chosen to minimize effector functions (like ADCC or CDC), focusing the mechanism purely on ligand blockade.