An immunoglobulin G1 (IgG1) bispecific antibody targeting both epidermal growth factor receptor (EGFR; HER1; ErbB1) and leucine-rich repeat-containing G-protein coupled receptor 5 (LGR5), with potential antineoplastic activity. Upon administration, petosemtamab simultaneously targets and binds to both EGFR and LGR5, thereby inhibiting the activation of both EGFR- and LGR5-mediated signaling pathways. This results in the inhibition of tumor cell proliferation. EGFR, a receptor tyrosine kinase (RTK) upregulated and/or mutated in a variety of tumor cell types, plays an important role in tumor cell proliferation. LGR5, a member of the Wnt signaling pathway, is a cancer stem cell (CSC) receptor overexpressed on certain cancer cells; it plays a key role in CSC proliferation and survival.