The purpose of this prospective, single-center, single-arm, open-label II phase observation clinical trial is to evaluate the efficacy and safety of Pembrolizumab immunoadjuvant therapy in patients with stage III-IVA oral squamous cell carcinoma. The primary end point is the pathological tumor remission rate of the primary tumor and regional lymph nodes after neoadjuvant immunotherapy (pTR-2: the proportion of necrotic tumor cells, keratin fragments and giant cells in tissue sections > 50%). The secondary endpoints are 1-year disease-free survival (DFS), 1-year overall survival (OS) and the incidence of adverse events, compared with historical data. In addition, we will check the relevant immune indicators, such as PD-L1 and CPS scores.

Inclusion Criteria:

• Age 18-70
• Male and female
• Patients histologically or cytologically difined as oral cavity squamous cell carcinoma
• According to the American Joint Committee on Cancer ( AJCC 8th Edition ) , patients with resectable stage III-IVA OCSCC
• ECOG performance status ≤ 1
• Patients with normal bone marrow and organ function as defined below:

Blood routine examination:

1. Absolute neutrophil count ≥ 1.5×109/L;
2. Platelets ≥ 100.0×109/L;
3. Hemoglobin ≥ 9.0 g/dL.

Liver function:

1. Totle bilirubin ≤ 2.0×ULN(Upper Limit Of Normal);

2. Alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase

   • 2.5×ULN;

3. Albumin ≥ 2.8g/dL.

Renal function:

(1)Creatinine clearance rate > 60.0ml/min.

Coagulation function:

(1)International Normalized Ratio ≤ 1.5；Activated Partial Thromboplastin Time ≤ 1.5×ULN

• Prior to and during study, and lasting 120 days for the final utilization of pembrolizumab, patients approve of contraception
• Patients voluntarily agree to participate in the study and sign the informed consent form

Exclusion Criteria:

• Prior treatment for OCSCC (sugery, immunotherapy, radiotherapy, chemotherapy)
• Patients with metastatic OCSCC with an unknown primary tumor site
• Patients with infectious disease: AIDS, hepatitis, active tuberculosis
• Received a live vaccine within 30 days prior to the first dose of pembrolizumab. Examples of live vaccines include, but are not limited to, the following: measles, mumps, rubella, varicella/zoster, yellow fever, rabies, Bacillus Calmette-Guérin ( BCG ), typhoid vaccine, or attenuated flu vaccine
• 5.Has a diagnosis of immunodeficiency or is receiving systemic steroid therapy (in dosing exceeding 10 mg daily of prednisone equivalent) or any other form of immunosuppressive therapy within 7 days prior to the first dose of pembrolizumab
• Currently receiving any other investigational agents
• Has a history of allergic reactions attributed to compounds of similar chemical of biologic composition to pembrolizumab or other agents used in the study
• Patients with ongoing or active infectoin requiring systemic therapy, symptomatic congestive heart failure, unstable angina pectoris, cardiac arrhythmia, underlying pulmonary disease, or psychiatric illness/social situations that would limit compliance with study requirements
• Has a or more active autoimmune disease
• Has a history( non-infectious ) pneumonitis that required steroids or current pneumonitis

Patients with stage III-IVA oral squamous cell carcinoma.(See Eligibility Criteria)