This is a prospective, single-center phase II study evaluating sintilimab plus chemotherapy as induction therapy for unresectable stage IIIC non-small cell lung cancer (NSCLC). Treatment-naive eligible patients who signed informed consent were enrolled after MDT screening. Patients received 4 cycles of sintilimab 200 mg intravenously every 3 weeks combined with chemotherapy. Post-treatment MDT evaluation was performed. Resectable patients underwent primary tumor resection and mediastinal lymph node dissection 4-6 weeks after the 4th cycle. Postoperative supraclavicular radiotherapy and guideline-recommended adjuvant therapy were determined by MDT and investigators. Unresectable patients received concurrent chemoradiotherapy.

Inclusion Criteria:

Signed written informed consent prior to any study-related procedures. Age ≥18 and ≤75 years, male or female. Histologically or cytologically confirmed non-small cell lung cancer (NSCLC). At least one measurable lesion per RECIST 1.1. Treatment-naive, initially unresectable stage IIIC NSCLC (UICC/AJCC 9th edition).

No known EGFR/ALK sensitive mutations. Willing to undergo re-evaluation for surgery and accept surgery if eligible. No absolute contraindications to surgery. ECOG performance status 0-1. Life expectancy >6 months. Adequate organ function. Negative pregnancy test for fertile females.

Exclusion Criteria:

Other malignancy within 5 years (except cured basal cell carcinoma, squamous cell carcinoma of skin, or carcinoma in situ).

Participation in another interventional clinical study within 4 weeks. Prior anti-PD-1/PD-L1/PD-L2 or other immune checkpoint inhibitor therapy. Systemic anti-tumor Chinese patent medicine or immunomodulatory drugs within 2 weeks.

Active autoimmune disease requiring systemic therapy within 2 years. Systemic glucocorticoid or immunosuppressive therapy within 7 days. History of allogeneic organ transplant or hematopoietic stem cell transplant. Hypersensitivity to sintilimab or any excipient. Inadequate recovery from prior interventions (≥Grade 2). Known HIV infection. Untreated active HBV infection; active HCV infection. Live vaccine within 30 days. Pregnant or lactating women. Severe uncontrolled systemic disease (cardiac, pulmonary, hepatic, renal, infectious, etc.).