Programmed Death-Ligand 1 Copy Number Alteration as an Adjunct Biomarker of Response to Immunotherapy in Advanced NSCLC

Introduction: This study aimed to evaluate the value of programmed death-ligand 1 (PD-L1) copy number (CN) alteration as an additional biomarker to standard immunohistochemistry (IHC) in predicting response to immune checkpoint inhibitor (ICI) therapy in advanced NSCLC.Methods: Before ICI monotherapy, tumor PD-L1 CN alteration (gain, neutral, or loss) was called using whole-exome sequencing data and compared with IHC results (tumor proportion score >50, 1-49, or 0). Progression-free survival (PFS) and overall survival were correlated with both biomarkers. In addition, the impact of CN alteration was further evaluated in two independent cohorts using next generation sequencing panel.Results: A total of 291 patients with advanced-stage NSCLC met the study inclusion criteria. Although the IHC classifi-cation distinguished the best responsive group (tumor proportion score > 50), the CN-based classification distinguished the worst responsive group (CN loss) from the others (PFS, p = 0.020; overall survival, p = 0.004). After adjusting for IHC results, CN loss was an independent risk factor for progression (adjusted hazard ratio = 1.32, 95% confidence interval: 1.00-1.73, p = 0.049) and death (adjusted hazard ratio = 1.39, 95% confidence interval: 1.05-1.85, p = 0.022). A risk classification system was developed on the basis of IHC and CN profiles, which outperformed the conventional IHC system. In the valida-tion cohorts, CN loss determined by next-generation sequencing panel was independently associated with worse PFS after ICI treatment, revealing its practical value.Conclusions: This is the first study to directly compare CN alterations with IHC results and survival outcomes after anti-PD-(L)1 therapy. Tumor PD-L1 CN loss can serve as an