Lumretuzumab is a humanized monoclonal antibody designed to target the HER3 (ERBB3) receptor, which plays a key role in the activation of signaling pathways involved in cell growth and survival, particularly in cancers with dysregulated HER signaling. It is primarily investigated for its potential in oncology, especially in tumors that overexpress HER3 or rely on HER3-mediated pathways for progression, such as certain types of breast, ovarian, lung, and gastric cancers.

By binding to HER3, lumretuzumab blocks the interaction between HER3 and its ligand neuregulin, thereby inhibiting downstream signaling through the PI3K/AKT pathway—a critical route for cancer cell survival and resistance to therapy. It has been studied both as a monotherapy and in combination with other targeted agents, such as EGFR or HER2 inhibitors, to enhance antitumor activity and overcome resistance mechanisms.

Clinical development has focused on evaluating its safety, pharmacokinetics, and efficacy in patients with advanced solid tumors. While early-phase trials showed target engagement and some biological activity, development has faced challenges related to efficacy and tolerability, leading to a reevaluation of dosing strategies and combination regimens. Despite these hurdles, lumretuzumab remains a tool for understanding HER3 biology and a candidate for further optimization in targeted cancer therapy.