This research study is looking at two ways to treat a type of cancer called head and neck squamous cell carcinoma. This cancer can come back after surgery or be a new cancer, not spread from somewhere else. The study compares two treatments after surgery: pembrolizumab and the usual treatment, which is chemotherapy (using drugs like cisplatin and carboplatin) plus radiation therapy. Pembrolizumab is a type of medicine called an immunotherapy drug that helps your body's immune system fight cancer. Radiation therapy uses strong beams of energy to kill cancer cells.

Key Points to Consider:

• Participation requires regular visits for treatment over a year. Pembrolizumab is given every 6 weeks, while chemotherapy with radiation is weekly.
• The study checks survival rates and side effects for both treatments. Pembrolizumab might have fewer side effects than chemotherapy and radiation.
• After finishing the treatment, patients will have follow-up check-ups every 6 months for up to 5 years.

Participants must be between 18 and 79 years old, have specific cancer conditions, and meet other health criteria. It's important to understand the potential risks, and you should be willing to sign a consent form to join the study.