This single arm study is designed to demonstrate the feasibility of a radically different approach for an exceptionally high-risk subset of MES with widely metastatic disease (WMES). We incorporate the use of evolutionary principles that apply to species and population dynamics as related to adaptation and extinction to populations of cancer cells that similarly adapt and that we are attempting to make extinct, resulting in a cure for the patient. Such principles include an initial intense first strike to deplete the bulk of the cancer cells, followed by a series of sequential second strikes towards eliminating residual, resistant populations, followed by a prolonged period of maintenance chemotherapy to eliminate any remnant cells, using agents generally regarded to be active against newly diagnosed ES.

This study is researching an experimental drug called fianlimab (also called REGN3767), combined with a medication called cemiplimab compared against cemiplimab combined with placebo (a placebo looks like a treatment but does not contain any real medicine), collectively called "study drugs" in this form.

The study is focused on participants with head and neck cancers who have not been previously treated for head and neck cancer that has come back or spread to other parts of the body, referred to as recurrent or metastatic (R/M) head and neck squamous cell carcinoma (HNSCC).

The study is looking at several other research questions, including:

* What side effects may happen from taking the study drugs
* How much of each study drug is in the blood at different times
* Whether the body makes antibodies against the study drug(s) individually (which could make the study drugs less effective or could lead to side effects)
* Compatible research to better understand the study drugs and HNSCC