This study is comparing **Dostarlimab**, a type of medicine, with a **placebo** (a harmless pill with no effect) to see how safe and effective it is for adults with a type of cancer called **HNSCC** (Head and Neck Squamous Cell Carcinoma). This cancer affects areas like the mouth and throat. Participants need to have completed a combination of treatments called **CRT** (Cisplatin plus Radiotherapy) and should not have cancer that has spread to other parts of the body.

Key Points:

• The study length is not specified, but participants must not have had major surgery or certain treatments recently.
• Participants must have good organ function and not have certain other health conditions.
• Women who are pregnant or breastfeeding cannot participate.

This study is for participants who have a newly diagnosed unresected cancer and meet specific health criteria. It's important to know that previous treatments for head and neck cancer, other than CRT, make you ineligible. Discuss with your doctor if considering participation, especially regarding any previous treatments or existing health conditions.