Surgery With or Without Neoadjuvant Treatment of SBRT Plus Chemoimmunotherapy in Resectable Locally Advanced Oral and HPV-unrelated Oropharyngeal Squamous Cell Carcinoma

The inclusion criteria for this study are as follows: * Histologically and/or cytologically confirmed treatment-naïve oral squamous cell carcinoma or HPV-negative oropharyngeal squamous cell carcinoma. * Clinical stage III -Ⅳa (8th edition of AJCC). * Age: 18 to 75 years old. * According to the Eastern Cooperative Oncology Group (ECOG) criteria (with a performance status score of 0 or 1). * Good organ function. * Expected survival time: ≥ 3 months. * The patient has signed the informed consent form and is willing and able to comply with the study's scheduled visits, treatment plans, laboratory tests, and other research procedures. * Females of childbearing potential must have a negative urine or serum pregnancy test within 7 days prior to enrolment and must agree to use highly effective contraceptive measures during the study period and for at least 60 days after the last dose (including chemotherapeutic drugs and Tislelizumab). * If the female partner of a male subject is still of childbearing potential, the male subject must agree to use highly effective contraceptive measures during the study period and for at least 60 days after the last dose. Exclusion Criteria: * Patients with concurrent other malignant tumors * Patients with known or suspected autoimmune diseases, including dementia and epilepsy. * Patients with severe mental disorders at the same time * Patients with necrotic lesions who are assessed by the investigator as having a risk of massive hemorrhage * Patients with severe heart disease or pulmonary dysfunction, and those with cardiac or pulmonary function grade ≤ 3 (grade 3 inclusive) * Patients with laboratory test results that do not meet the relevant criteria within 7 days prior to enrollment * Received systemic or local glucocorticoid therapy within 4 weeks prior to enrollment * Patients with comorbidities requiring long-term treatment with immunosuppressive drugs, or requiring systemic or local administration of corticosteroids at immunosuppressive doses. * Patients with active tuberculosis (TB), who are receiving anti-tuberculosis treatment or have received anti-tuberculosis treatment within 1 year prior to screening. * A history of prior use of anti-Tislelizumab, anti-PD-L1 antibodies, anti-PD-L2 antibodies, or anti-CTLA-4 antibodies (or any other antibodies targeting T-cell co-stimulation or checkpoint pathways). * Subjects with any active autoimmune diseases or a history of autoimmune diseases (including but not limited to: interstitial pneumonia, uveitis, enteritis, hepatitis, hypophysitis, nephritis, hyperthyroidism, hypothyroidism); subjects with vitiligo or those whose childhood asthma has been completely relieved and who do not require any intervention in adulthood are eligible for enrollment; those with asthma requiring medical intervention with bronchodilators are not eligible for enrollment. * HIV-positive subjects * Positive for HBsAg with concurrent positive HBV DNA copy number (quantitative test ≥ 1000 cps/ml); positive for chronic hepatitis C on blood screening (HCV antibody positive) * Received any anti-infective vaccines (such as influenza vaccine, varicella vaccine, etc.) within 4 weeks prior to enrollment * Pregnant women with positive pregnancy test results among females of childbearing potential and lactating women.