A Prospective Randomized Controlled Study of Immune Checkpoint Maintenance Therapy After Radiotherapy and Chemotherapy for Locally Advanced Head and Neck Tumors Based on Peripheral Blood CD8Tex Detection in Peripheral Blood

The goal of this prospective, randomized, single-blind controlled clinical study is to explore the efficacy of maintenance therapy with Sintilimab after chemoradiotherapy in locally advanced head and neck squamous cell carcinoma. The main questions it aims to answer are: How works well the Sintilimab was in the treatment group？ How safe the Sintilimab is？ Participants will intravenous Sintilimab or placebo (a look-alike substance that contains no active drug) within 1 month after the end of chemoradiotherapy, and 21 days is a cycle. Blood tests, electrocardiogram are rechecked every 2 cycles, and CT was rechecked every 4 cycles to evaluate toxicity and side effects and recurrence. Researchers will compare invention group to control group to see if the Sintilimab works well.