Study to Evaluate the Efficacy and Safety of Adjuvant Tislelizumab in High-Risk Stage I NSCLC

Inclusion Criteria: * Able to provide written informed consent form (ICF) and agree to follow study requirements and assessment schedule. * Aged 18 years or older. * Histologically confirmed stage I non - small cell lung cancer (AJCC 9th edition), with tumor size 2cm \<= T \<=4cm. * Postoperative pathological report shows at least one high-risk factor (visceral pleural invasion, lymphovascular invasion, STAS, poorly differentiated status, high-grade invasive adenocarcinoma (any structure + high grade structure \>=20%, including solid, micropapillary, or complex glands)). * ECOG performance status 0 or 1. * PD-L1 expression \>=1%. * No EGFR/ALK sensitive mutations. * Achieved complete resection (R0) . * Within 8 weeks after surgery, with full recovery from operation. * Adequate organ function. Exclusion Criteria: * Any previous treatment for current lung cancer, including radiotherapy and systemic anti-tumour therapies (chemotherapy, immunotherapy, targeted therapy, anti-angiogenesis therapy, etc.). * Prior chest radiotherapy (including lung, oesophageal, mediastinal, or breast cancer). * Patients with large - cell neuroendocrine carcinoma (LCNEC) or mixed - subtype non - small - cell lung cancer with small - cell components. * With EGFR/ALK sensitive mutations. * Underwent segmentectomy or wedge resection only. * Tumours involving main bronchi, or with obstructive pneumonia/atelectasis (partial or whole lung). * Active autoimmune disease or history of relapsing autoimmune disease. * History of interstitial lung disease, drug-induced interstitial lung disease, or radiation pneumonitis needing hormone therapy, or current active interstitial lung disease, or on relevant treatment/intervention. * Any condition needing systemic corticosteroid (\> 10 mg/d prednisone or equivalent) or other immunosuppressant within 14 days before randomisation * Used other approved systemic immunomodulators (interferon, interleukin - 2, tumour necrosis factor, thymopentin, thymosin α1, etc.) within 4 weeks before first dose. * Herbs used for cancer control within 14 days before first study * Live/attenuated vaccine receipt within 4 weeks before enrollment, or plan to receive during study or within 5 months after last tislelizumab dose. * History of significant disease or conditions affecting organ/system function, per investigator's judgment. * Severe chronic/active infection needing systemic antibacterial, antifungal, or antiviral therapy (e.g., tuberculosis) within 14 days before first study-drug dose. ·Known HIV infection. * Allogeneic stem - cell/organ transplant history. * Active malignancy within 2 years before enrollment, except the specific cancer studied and locally recurrent cancers cured (e.g., excised basal/squamous - cell skin cancer, superficial bladder cancer, cervical/ breast carcinoma in situ). * Specific conditions and/or alcohol/drug abuse or dependence that may hinder drug administration, affect outcome interpretation, or increase complication risks. * Pregnant/breastfeeding women, or men/women planning to conceive during the study. * Participation in another interventional clinical study (except observational studies or follow-up phases).