This is a Phase 3 study comparing two treatments for certain types of head and neck cancer. The treatments studied are petosemtamab plus pembrolizumab, and pembrolizumab alone. Pembrolizumab is a type of medicine called a checkpoint inhibitor, which helps the immune system fight cancer. Participants must be at least 18 years old, have specific types of cancer, and not have received certain previous treatments. The study is randomized (participants are assigned by chance to different treatments) and open-label (patients and doctors know which treatment is being given).

• The study requires multiple visits and tests to monitor treatment effects.
• Participants may receive compensation for their time and involvement.
• Risks could include side effects from the treatments, which will be monitored.

Individuals interested in participating should discuss with their doctor to ensure they meet all eligibility criteria.