Study of Sinibolimab Combined with Lenvatinib As Neoadjuvant Therapy for Locally Advanced Unresectable Differentiated Thyroid Carcinoma

Inclusion Criteria: * Histologically confirmed newly diagnosed or recurrent locally advanced (T4N1M0) differentiated thyroid carcinoma with an estimated risk of R2 resection. Performance Status (PS) score of 0-1. Age ≥ 18 years. Measurable lesions according to RECIST 1.1 criteria. Normal function of major organ systems. Exclusion Criteria: * Intratracheal airway tumors. Complete carotid artery encasement/invasion. Full-thickness infiltration of the esophageal wall. Arterial thrombosis/cancer thrombus. Active hemoptysis (bright red blood ≥ 1/2 teaspoon) or other uncontrolled bleeding within 21 days prior to study enrollment. History of prior neck radiotherapy. Previous treatment with Lenvatinib or immunotherapy. Participants with \> 1+ proteinuria on urine dipstick will undergo 24-hour urine collection for quantitative assessment of proteinuria. Participants with urine protein ≥ 1g/24 hours will be ineligible. Active, known, or suspected autoimmune diseases. Participants requiring long-term systemic corticosteroid therapy. Participants using bronchodilators, inhaled corticosteroids intermittently due to COPD or asthma, or those receiving local corticosteroid injections may be eligible. Active unstable angina and/or congestive heart failure. New-onset myocardial infarction within the last 6 months.