Global Phase 3 Trial Design and Mechanism of Petosemtamab

The 'LiGeR-HN1 (NCT06525220)' Phase 3 trial, sponsored by Genmab's subsidiary Merus, targets patients with recurrent/metastatic PD-L1-positive (Combined Positive Score, CPS 1 or higher) head and neck squamous cell carcinoma (HNSCC). This trial will evaluate the combination therapy of petosemtamab (MCLA-158), a bispecific antibody, and Keytruda (pembrolizumab), an anti-PD-1 immune checkpoint inhibitor from MSD, compared to Keytruda monotherapy. Petosemtamab utilizes an innovative mechanism by simultaneously targeting EGFR on tumor cell surfaces and LGR5, an antigen found on cancer stem cells, inducing receptor internalization and degradation, and activating antibody-dependent cellular cytotoxicity (ADCC).

Differentiation from Existing Standard of Care

Currently, Keytruda monotherapy or combination therapy with chemotherapy has become the standard of care (SoC) in the first-line treatment setting. However, these treatments still face significant limitations, including low response rates and limited progression-free survival (PFS). Petosemtamab is designed to maximize the efficacy of immune checkpoint inhibitors by strongly inhibiting tumor growth and metastasis while simultaneously enhancing the efficiency of the immune response, creating a synergistic effect. In particular, it has demonstrated a high objective response rate (ORR) of over 60% in a previous Phase 2 trial in first-line treatment patients, generating significant market expectations.

FDA Regulatory Approval Pathway and Breakthrough Therapy Designation

The U.S. Food and Drug Administration (FDA) recognized the significant clinical utility of petosemtamab and granted it Breakthrough Therapy Designation (BTD) in May 2024 for monotherapy in patients who had progressed after platinum-based chemotherapy. Subsequently, on February 18, 2025, the FDA approved a second BTD for the combination of petosemtamab and Keytruda for the first-line treatment of PD-L1-positive recurrent/metastatic HNSCC. These designations provide a crucial regulatory foundation that could significantly shorten the time to commercialization after the completion of Phase 3 trials through accelerated approval or priority review.

Commercialization Acceleration Through Merger and Acquisition

Genmab A/S, a global biotechnology company based in Denmark, recognized the commercial value of petosemtamab, a late-stage pipeline asset and BTD product from Merus, and agreed to acquire Merus for approximately $8.0 billion (USD) in cash, or $97.00 per share, on September 29, 2025. The acquisition was successfully completed in late December 2025, and Merus was delisted from the NASDAQ. Through this major deal, Genmab is strongly accelerating the transition to a self-commercialization model by completing the global Phase 3 trial of petosemtamab based on its independent development capabilities and financial resources.

Market Outlook and Significance for Improving Patient Quality of Life

The global HNSCC treatment market is estimated at approximately $2.35 billion in 2025 and is projected to reach up to $5.65 billion by 2035, driven by an aging population and an increase in HPV infection rates. The emergence of a new immune combination therapy that minimizes the side effects of painful conventional chemotherapy while significantly improving survival rates represents a major milestone that will transform the treatment paradigm for head and neck cancer. If the clinical trials are successful, Genmab will secure annual blockbuster sales of hundreds of millions of dollars and become a key player in rapidly reshaping the existing standard of care market.