Immunotherapy resistance in non-small cell lung cancer: from mechanisms to therapeutic opportunities

This review provides a comprehensive synthesis of current knowledge on immunotherapy resistance in non-small cell lung cancer (NSCLC), a disease that accounts for approximately 85% of all lung cancer cases and remains the leading cause of cancer-related death worldwide. Although immune checkpoint inhibitors (ICIs) have significantly improved survival for a subset of patients with advanced NSCLC, over 70% of cases ultimately exhibit primary or acquired resistance, underscoring the urgent need to understand the underlying mechanisms. The review categorizes resistance into tumor-intrinsic and tumor-extrinsic processes and provides an in-depth mechanistic analysis of how factors such as tumor antigen loss, impaired antigen presentation, cGAS-STING pathway dysregulation, metabolic reprogramming in tumor microenvironment (TME), immune cell exhaustion, and microbiomes collectively contribute to immune escape. In parallel, the influence of the lung and gut microbiome on shaping immunotherapy responses is discussed, with emphasis on microbial dysbiosis, immunosuppressive metabolite production, and TME remodeling. Therapeutic strategies to overcome resistance are also discussed, including combination approaches involving chemotherapy, radiotherapy, and antiangiogenic agents, as well as epigenetic modulators (HDAC and BET inhibitors). Moreover, the review explores bispecific antibodies, antibody-drug conjugates, and small-molecule agents that enhance T cell function or disrupt immunosuppressive signaling networks. By integrating insights from preclinical models and clinical trials, the review underscores the necessity of biomarker-guided patient stratification, combination immunotherapy approaches, and interventions that restore tumor immunogenicity. It concludes that a multipronged therapeutic strategy, one that addresses both immune evasion and TME-induced suppression, holds the greatest promise for improving response durability and advancing personalized immunotherapy for NSCLC.