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.