Genmab Jumps About 30% as Petosemtamab Cuts Risk of Death by Half in Phase 3 Head and Neck Cancer Trial

GMAB said petosemtamab plus pembrolizumab, Keytruda from MRK, met both primary endpoints, overall survival and objective response rate, in the Phase 3 LiGeR-HN1 trial in first-line PD-L1-positive recurrent or metastatic head and neck squamous cell carcinoma. At the first interim analysis the combination cut the risk of death by 50% versus pembrolizumab alone, a hazard ratio of 0.50. The company's announcement put the 95% confidence interval at 0.37 to 0.67 and the odds ratio for response at 3.17, and said no new safety signals were identified.

Petosemtamab is a bispecific antibody targeting EGFR and LGR5 that Genmab gained through its roughly $8 billion acquisition of Merus, which closed in December 2025. It already holds FDA Breakthrough Therapy Designation in this setting. Genmab said it plans to engage global regulators and present the full data at a future medical meeting; it did not give a filing date.

Investors treated the readout as a defining result. The U.S.-listed shares were up 16% early in the session and later about 30%, reaching an all-time high, on volume of 19.66 million shares against a three-month average of about 4.14 million.

The open questions are the ones an interim readout leaves. Median survival and response rates were not disclosed, the trial is open-label, and the commercial opportunity depends on how regulators weigh the data against the current pembrolizumab standard. A second trial, LiGeR-HN2, in later-line patients, is still running.