Evaluating the Efficacy and Safety of Pembrolizumab Plus Standard Chemotherapy in the Neoadjuvant Treatment of Local Advanced (LA) HNSCC

Inclusion Criteria: 1. Patients with stage IIIA-IVB head and neck squamous cell carcinoma confirmed by histology and/or cytology; 2. Have not received immunotherapy in the past; 3. The researchers believe that he can safely receive pembrolizumab combined with chemotherapy or neoadjuvant chemotherapy; 4. Age ≥18 years; 5. ECOG 0-2; 6. Measurable disease as defined by RECIST v1.1; 7. Organs function normally; 8. Female and male participants of reproductive potential must agree to use appropriate contraception throughout the study period and for 180 days after the last study treatment; 9. Male participants must not donate sperm throughout the study and for 180 days after the last study treatment. Exclusion Criteria: 1. Presence of distant metastasis; 2. Female subjects with a positive urine pregnancy test within 72 hours before the start of the study or within 24 hours after starting radiation therapy (with or without cisplatin); 3. received a live vaccine within 30 days before enrollment; 4. Diagnosed with immunodeficiency or receiving systemic steroid treatment or any other form of immunosuppressive treatment within 7 days before enrollment; 5. Have imaging detectable (even if asymptomatic and/or previously treated) central nervous system metastases and/or cancerous meningitis; 6. Have undergone surgery before commencing the study or have failed to recover adequately from toxicity or complications resulting from the intervention; 7. Previous allogeneic tissue/solid organ transplant; 8. Severe hypersensitivity reaction (≥Grade 3) to pembrolizumab or any of its excipients, radiotherapy, platinum, paclitaxel, 5-FU or their analogs; 9. Have an active autoimmune disease requiring systemic therapy in the past 2 years; 10. History of (non-infectious) pneumonia requiring steroid treatment; 11. Have a history of human immunodeficiency virus (HIV) infection; 12. Have a history of hepatitis B or be positive for hepatitis B virus (defined as a positive reaction to hepatitis B surface antigen \[HBsAg\]) or active hepatitis C (defined as detection of hepatitis C virus \[HCV\] ribonucleic acid). 13. Have any medical history, treatment, or laboratory abnormalities that could confound the study results, interfere with participant participation throughout the study, or be detrimental to the best interests of the participant (e.g., Hashimoto's thyroiditis, etc.); 14. Have a known history of mental illness or substance abuse disorder