This study is looking at a new drug called fianlimab (also known as REGN3767) to see if it works better with another drug called cemiplimab compared to cemiplimab with a fake treatment (placebo) on people with head and neck cancer. The cancer can be recurrent (comes back) or metastatic (spreads to other parts of the body). The study wants to learn what side effects might happen, how much of the drug gets into the blood, and if the body fights against the drug.

• The study will include people with specific types of head and neck cancers who haven't had treatment for the cancer coming back or spreading.
• It will check if participants have certain health or medical conditions before they can join.
• Participants should not have had some specific medicines or conditions recently to join the study.

If you qualify and join, you will help researchers understand these drugs better, but you should consider the possible risks and benefits first.