Pembrolizumab is a type of immunotherapy that helps the body's immune system fight cancer. In this study, researchers are testing if pembrolizumab alone works better than the usual treatment of chemotherapy (using drugs like cisplatin and carboplatin) combined with radiation therapy. This study is for patients whose head and neck squamous cell carcinoma, a type of cancer, has returned or who have a new cancer in the same area.

Key Points:

• Participants will be randomly assigned to receive either pembrolizumab or the usual chemotherapy/radiation treatment after surgery.
• The study involves multiple visits for treatments and scans over a period of up to one year, with follow-up visits every six months for five years.
• Participants must be between 18 and 79 years old and meet specific health requirements.

The goal is to see if pembrolizumab helps patients survive longer without their cancer coming back. Participants are observed closely for any side effects or disease progression. This study may help improve cancer treatment options in the future.