Key Highlights

  • Genmab (NASDAQ:GMAB) closed up 28.25% on October 28, 2026, after a Phase 3 trial of petosemtamab showed a 50% reduction in the risk of death in head and neck cancer.
  • The shares touched +29.9% intraday, per published market data, as investors reacted to a result for Genmab (NASDAQ:GMAB) from the company release as summarized. Details beyond the headline are still needed.
  • Petosemtamab was tested together with pembrolizumab and compared with pembrolizumab alone, so the result measures the added benefit of the new therapy on top of the standard drug.
  • A 50% reduction in the risk of death is a relative measure. Absolute survival times, safety data and regulatory plans were not in the summary reviewed.

What the Phase 3 Result Showed

Genmab (NASDAQ:GMAB) said on October 28, 2026 that a Phase 3 trial of its investigational therapy petosemtamab met its goal in head and neck cancer. The company reported a 50% reduction in the risk of death for patients who received petosemtamab plus pembrolizumab, compared with pembrolizumab alone. The shares closed up 28.25% and reached +29.9% intraday, according to published market data. The details come from the company release as summarized, and the full data set was not reviewed, so figures such as median survival, confidence intervals and side effects are not covered here. Genmab is a Danish biotech that trades in the United States as depositary shares.

Why a 50% Risk Reduction Matters

A 50% reduction in the risk of death means the hazard ratio for death was about 0.5: at any given time, patients on the combination faced roughly half the risk of dying compared with patients on pembrolizumab alone. It is a relative figure, not a promise that half of patients survive. Phase 3 trials are the large, controlled studies regulators usually rely on, so a clear survival benefit can support an application for approval. Head and neck cancer is a difficult disease with limited treatment options, which is why a survival signal in a controlled setting moves stocks sharply. The pembrolizumab-only arm is the control, which makes the comparison a direct test of added value.

Risks and What to Watch

A single press release is not an approval. Genmab (NASDAQ:GMAB) still has to present the full data, show that side effects are manageable and win regulatory review, and the timing of any filing was not disclosed in the information reviewed. Large one-day gains can also reverse if the detailed data disappoint, and the stock now carries higher expectations. Watch for a medical-meeting presentation, regulatory filing plans, and any comparison with rival head and neck cancer treatments. Investors should also remember that the broader market was cautious, with Nasdaq-100 futures down 1.2% at 4:09 a.m. ET on October 29. Rivals developing head and neck therapies will also study the data closely.

Where Things Stand

A strong survival result is the reason. Genmab (NASDAQ:GMAB) rose 28.25% on October 28, 2026 after a Phase 3 trial of petosemtamab with pembrolizumab reported a 50% reduction in the risk of death versus pembrolizumab alone in head and neck cancer. The market is rewarding a clear efficacy signal, but safety detail, absolute survival data and regulatory plans are still to come. The next catalysts are the full data presentation and any filing timeline.