This study is testing a drug called Dostarlimab against a fake medicine called a Placebo for people with a type of head and neck cancer called HNSCC (Head and Neck Squamous Cell Carcinoma). Dostarlimab is a medicine that helps the immune system find and attack cancer cells. To join, patients must have a new diagnosis of HNSCC that cannot be removed with surgery, and they must have finished treatment with a drug called Cisplatin and radiation. They must also have good organ function and not have cancer in other areas like the nose or sinuses.

• Participants must have completed specific cancer treatments before joining.
• Exclusion for those with certain other medical conditions or past treatments.
• Participants cannot be pregnant or planning to have children soon.

This study helps doctors understand more about how well Dostarlimab works and how safe it is for treating this type of cancer. If you're eligible, it's important to know there might be risks, and you should discuss with your doctor if this study is right for you.