The Efficacy and Safety of Sintilimab Plus Chemotherapy in Surgical Conversion for Patients With Unresectable Stage IIIB-IIIC NSCLC: A Prospective, Single-Arm, Phase II Study

Inclusion Criteria: * 1\. Patients voluntarily participate in this study and sign informed consent forms (including consent for relevant testing of collected biological samples). 2\. Histologically or cytologically confirmed NSCLC with no prior antitumor therapy (including systemic medications or local treatments). 3.Treatment-naïve patients with unresectable stage IIIB-IIIC NSCLC. 4. Evaluated by a multidisciplinary team (MDT): Surgical resection is not the current preferred treatment option, but radical resection of the primary lung lesion is feasible after induction chemoimmunotherapy, and metastatic contralateral/supraclavicular lymph nodes (if present) are amenable to definitive radiotherapy. 5\. Aged 18-75 years, regardless of gender. 6. ECOG performance status 0-1. 7. At least one measurable lesion per RECIST v1.1 criteria. 8. All suspicious mediastinal lymph nodes (e.g., pathologically enlarged or PET-CT-suggested malignancy) must undergo pathological confirmation via endobronchial ultrasound (EBUS), thoracoscopy, or mediastinoscopy if technically feasible. 9\. Pulmonary function (e.g., FVC, FEV1, TLC, FRC, DLco) deemed adequate for planned lung resection by MDT assessment. 10\. Absence of comorbidities that would elevate surgical risk to unacceptable levels. 11\. Adequate organ function within 14 days prior to enrollment (no blood components, growth factors, or corrective therapies allowed during this period): Absolute neutrophil count ≥1.5×10⁹/L, Platelets ≥100×10⁹/L, Hemoglobin ≥90 g/L, Serum albumin ≥35 g/L TSH ≤1×ULN, Total bilirubin ≤1.5×ULN, ALT/AST ≤3×ULN, INR ≤1.5 or PT ≤1.5×ULN, Serum creatinine ≤1.5×ULN 12. Non-sterilized or premenopausal female patients must use contraception (e.g., IUD, oral contraceptives, condoms) during the study and for 3 months post-treatment. Non-sterilized females must have a negative serum/urine HCG test within 72 hours before enrollment, be non-lactating, and male patients with fertile partners must use effective contraception during the trial and for 3 months after the last dose. Exclusion Criteria: * 1\. Patients with NSCLC harboring driver mutations (e.g., EGFR, ALK, ROS1). 2. Prior treatment with anti-PD-1, anti-PD-L1, anti-PD-L2, or anti-CTLA-4 therapies targeting T-cell co-stimulatory pathways. 3\. History of concurrent or other malignancies within the past 3 years (except cured basal cell carcinoma of the skin or cervical carcinoma in situ). 4\. Active hepatitis B/C with poor response to antiviral therapy. 5. Active autoimmune diseases or history of autoimmune disorders (including but not limited to autoimmune hepatitis, interstitial pneumonia, uveitis, enteritis, hypophysitis, vasculitis, nephritis, hyperthyroidism; vitiligo is permitted; childhood asthma resolved without intervention in adulthood is allowed; asthma requiring bronchodilators is excluded). 6\. Current use of immunosuppressants or systemic corticosteroids (\>10 mg/day prednisone equivalent) for immunosuppression within 2 weeks prior to enrollment. 7\. Poorly controlled hypertension (systolic BP ≥140 mmHg or diastolic BP ≥90 mmHg) or uncontrolled cardiac conditions: NYHA class ≥II heart failure, Unstable angina, Myocardial infarction within 1 year, Clinically significant supraventricular/ventricular arrhythmias requiring treatment, QTc \>450 ms (men) or \>470 ms (women). 8.Coagulopathy (INR \>2.0, PT \>16 s), bleeding tendency, or ongoing thrombolytic/anticoagulant therapy (prophylactic low-dose aspirin or LMWH is permitted). 9.Arterial/venous thrombotic events within 6 months (e.g., cerebrovascular accident, transient ischemic attack, deep vein thrombosis, pulmonary embolism). 10.Hereditary or acquired bleeding/thrombotic disorders (e.g., hemophilia, thrombocytopenia). 11\. Urinalysis showing proteinuria ≥++ with 24-hour urine protein \>1.0 g. 12. Active infection, unexplained fever ≥38.5°C within 7 days prior to treatment, or baseline leukocyte count \>15×10⁹/L. 13\. Congenital or acquired immunodeficiency (e.g., HIV infection). 14. Other factors deemed by the investigator to compromise patient safety or study outcomes (e.g., substance abuse, severe comorbidities, psychiatric disorders, or social circumstances affecting compliance).