The goal of this phase 2 trial is to evaluate the efficacy and safety of tislelizumab combined with intravenous chemotherapy and bronchial artery chemoembolization (BACE) as conversion therapy for patients with initially unresectable stage IIIA-IIIB non-small cell lung cancer (NSCLC). The main questions it aims to answer are:

• What is the 1-year event-free survival (EFS) rate with this treatment?
• Can this treatment improve tumor response and the chance of curative-intent resection?
• What adverse events occur during treatment?

Participants will receive tislelizumab, intravenous chemotherapy, and BACE for up to 4 cycles. Tumor response and resectability will be evaluated by imaging and multidisciplinary team (MDT) assessment every 2 cycles. Participants who become resectable may undergo surgery followed by postoperative treatment per protocol. Participants who remain unresectable after 4 cycles will receive guideline-recommended chemoradiotherapy followed by tislelizumab consolidation. Regular follow-up will be performed for efficacy and safety assessment.

Inclusion Criteria:

• Age 18 to 80 years
• Histologically or cytologically confirmed non-small cell lung cancer (NSCLC)
• Newly diagnosed, previously untreated stage IIIA-IIIB NSCLC according to the 9th edition TNM staging system
• Initially unresectable disease as determined by multidisciplinary team (MDT) assessment
• At least 1 measurable intrapulmonary lesion according to RECIST version 1.1
• Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1
• Forced expiratory volume in the first second (FEV1) > 1.0 L and > 40% of predicted normal value
• Estimated life expectancy of at least 3 months
• Adequate organ function
• Willingness to provide tumor tissue for pathology, molecular testing, and PD-L1 assessment before enrollment
• Women of childbearing potential must have a negative pregnancy test within 72 hours before the first dose and agree to use effective contraception during the study and for 3 months after the last dose of tislelizumab
• Men with partners of childbearing potential must agree to use effective contraception during the study and for 3 months after the last dose of tislelizumab
• Ability to understand and willingness to sign a written informed consent form

Exclusion Criteria:

• Prior local therapy for NSCLC, including radiotherapy or interventional therapy
• Known positive driver genomic alterations, including EGFR mutations, ALK rearrangements, ROS1 rearrangements, and MET exon 14 skipping alterations
• Distant organ metastasis
• History of another malignancy within the past 5 years
• Active autoimmune disease or history of autoimmune disease requiring systemic treatment
• Known allergy to any study drug or excipient
• Interstitial lung disease, non-infectious pneumonitis, chronic obstructive pulmonary disease, or other uncontrolled systemic diseases judged to interfere with study treatment
• Severe chronic or active infection requiring systemic antibacterial, antifungal, or antiviral therapy, including active tuberculosis
• Major surgery requiring general anesthesia within 4 weeks before first dose
• Any medical condition, alcohol or drug abuse, or dependence that may interfere with study treatment, interpretation of results, or increase treatment risk
• Participation in another interventional therapeutic clinical study
• Psychiatric illness or history of psychotropic drug abuse that may compromise study participation
• Any condition judged by the investigator to make the patient unsuitable for the study

Individual participant data are not planned to be publicly shared because of privacy, ethical, and legal considerations. The study includes sensitive clinical, imaging, and biomarker data, and the relatively small sample size may increase the risk of participant re-identification. Summary statistical data may be obtained from the Principal Investigator upon reasonable request and with approval from the Ethics Committee.