Adding Genmab's petosemtamab to Keytruda cut head and neck cancer death risk in half

The trial enrolled 699 patients, and at the first interim analysis the hazard ratio came in at 0.50. Copenhagen-based Genmab said on October 28 that adding its bispecific antibody petosemtamab to Merck's Keytruda (pembrolizumab) halved the risk of death compared with Keytruda alone in the Phase 3 LiGeR-HN1 trial. The patients had first-line recurrent or metastatic PD-L1-positive head and neck squamous cell carcinoma (HNSCC). Both primary endpoints, overall survival and objective response rate, were met, and they were met irrespective of HPV status.

The context explains why that number got attention fast. Everett Vokes, chair of the Department of Medicine and Physician-in-Chief at University of Chicago Medicine, told Clinical Trials Arena that LiGeR-HN1 is the first Phase 3 study in several years to come back positive in this patient population. In his view, recurrent or metastatic head and neck cancer can profoundly affect survival as well as some of the most essential parts of daily life, which makes better treatment an urgent need. He called the trial "a major milestone with the potential to redefine care."

Oncology service-line leaders and pharmacy teams would eventually decide how a new regimen enters practice, and for them two questions follow. What exactly did the trial show, and how much of it is settled?

Inside the LiGeR-HN1 numbers

LiGeR-HN1 (NCT06525220) is an open-label global trial. According to Clinical Trials Arena, it tested petosemtamab plus Keytruda against Keytruda alone in 699 patients. The figures released so far come from the first interim analysis, which an independent data monitoring committee reviewed.

Genmab's company announcement gives the full statistics and calls the survival improvement statistically significant and clinically meaningful. The overall survival hazard ratio was 0.50, with a 95% confidence interval of 0.37 to 0.67 and p<0.0001. Objective response had an odds ratio of 3.17, with a confidence interval of 2.06 to 4.89 and p<0.0001.

The response result adds weight to the survival result. Because the readout pairs a response endpoint with a survival endpoint, it gives two separate signals that point the same way. A response benefit on its own would likely carry less weight.

The baseline shows why the next disclosure matters so much. When median survival in recurrent or metastatic disease is around 10 to 12 months, even a modest number of added months would be a large share of a patient's expected survival. That absolute gain, more than the relative one, is likely to anchor value discussions at the pathway table.

A second drug on a familiar backbone

Petosemtamab is an investigational IgG1 bispecific antibody that targets two receptors: the epidermal growth factor receptor (EGFR) and LGR5, a leucine-rich repeat receptor. Bispecifics bind two different antigens, or two sites on one antigen, at the same time.

The class already has a foothold in solid tumors. A 2025 review in Frontiers in Immunology describes bispecifics as "next-generation antibodies" because they get around the limit of natural monoclonal antibodies, which bind only a single epitope. That review counts three bispecific antibodies approved for lung cancer. The first was amivantamab, initially approved for non-small cell lung cancer with EGFR exon 20 insertion mutations that had progressed on or after platinum-based chemotherapy. Petosemtamab would bring the approach into first-line head and neck cancer, alongside a checkpoint inhibitor rather than after chemotherapy.

The trial design shapes what adoption would look like. Petosemtamab was tested as an add-on to pembrolizumab rather than as a replacement for it. If regulators approve the combination on these data, the regimen would add an agent to Keytruda in first-line PD-L1-positive disease. Many cancer centers already treat these patients with pembrolizumab alone, and the trial's comparator arm maps directly onto that population. That makes the readout easier to translate into a pathway decision than a head-to-head trial against an unfamiliar control.

The benefit held regardless of HPV status, which suggests eligibility would depend on PD-L1 positivity without a separate cut by HPV. On safety, Genmab described the combination as generally well tolerated, with a profile consistent with each drug's known effects and no new safety signals. Petosemtamab also holds FDA Breakthrough Therapy Designation for this first-line combination.

The enthusiasm came quickly. BioSpace's Nick Paul Taylor reported that William Blair analysts called the result "exceedingly positive," and Truist Securities analysts described the survival finding as "highly compelling and potentially practice-changing." Clinical Trials Arena noted that analysts had branded the data "exceptional."

The strongest reason for caution comes from the trial itself. This is an open-label study at its first interim analysis, and only topline figures and a qualitative safety summary are public. That makes the full results, which Genmab plans to present at an upcoming medical meeting, an important next step.

The Merus deal starts paying back

Petosemtamab did not start out as a Genmab drug. The company got it through its $8 billion acquisition of Merus last year, a deal that Drug Discovery News said already appears to be paying off. Investors seemed to agree. Genmab's stock rose 29% to $57.57 in early trading on the day of the announcement, according to BioSpace.

The readout also completes what BioSpace called a clean sweep of victories in a high-stakes run of Genmab readouts. At the start of October, the company was preparing to share Phase 3 data on three candidates: Epkinly (epcoritamab), its AbbVie-partnered bispecific, in lymphoma; the antibody-drug conjugate rinatabart sesutecan (Rina-S) in ovarian cancer; and petosemtamab. Weeks later, all three had produced positive results.

Behind that run of results is a revenue problem. BioSpace described Genmab as bracing for patent losses on Darzalex, its cornerstone product, and betting its future on these three programs, with petosemtamab as an asset central to its growth plans. Seen that way, a first-line survival win does more than validate one molecule. It also suggests the price paid for Merus bought a drug that could help fill the gap Darzalex leaves.

In the announcement, CEO Jan van de Winkel called the LiGeR-HN1 results a defining milestone for Genmab and said they strengthen the company's view of petosemtamab as a potential first-in-class option in this cancer.

Regulators, a podium and three more trials

Genmab will submit the full results for presentation at a future medical meeting, and it plans to engage global regulatory authorities. It has not published a filing date.

Head and neck is also only the drug's first readout. Genmab is running the Phase 3 LiGeR-HN2 trial of petosemtamab in head and neck cancer patients at later lines of therapy, along with two Phase 3 trials in metastatic colorectal cancer. A positive LiGeR-HN2 could extend the drug beyond first-line PD-L1-positive patients. The colorectal trials could show whether the dual EGFR and LGR5 approach carries into a second tumor type.

The nearest milestone is the presentation of the full results at that medical meeting. Those fuller data will shape how quickly pathway committees put the combination on their agendas.