Fibrinogen alpha chain is associated with response to immune checkpoint inhibitors in non-small cell lung cancer: a multi-cohort discovery and validation study

Immune checkpoint inhibitors (ICIs) have improved outcomes in non-small cell lung cancer (NSCLC), yet reliable biomarkers to predict clinical response remain limited. This study aimed to identify and validate a clinically practical biomarker reflecting neoantigen-driven immunogenicity and associated with ICI efficacy in NSCLC. We conducted a multi-phase study integrating unbiased discovery, clinical validation, and preliminary mechanistic exploration. Multi-omics profiling of a prospective NSCLC cohort ( n = 28) integrated genomics, transcriptomics, and proteomics to identify fibrinogen alpha chain (FGA) as a top candidate. FGA was evaluated by quantitative immunohistochemistry in a training ( n = 93) and independent validation ( n = 78) cohort of patients with advanced NSCLC treated with ICIs. Multiplex immunofluorescence characterized FGA‑associated immune biology, and in vitro transcriptomic analysis explored transcriptional programs associated with FGA exposure. FGA expression positively correlated with tumor neoantigen expression ( r = 0.618, p < 0.001). In the training cohort, high FGA was associated with significantly prolonged progression-free survival (median PFS: 25.8 vs. 5.2 months; adjusted HR = 0.44, p = 0.003) and higher objective response rate (50.0% vs. 30.8%). These findings were confirmed in the independent validation cohort (median PFS: 38.0 vs. 14.4 months; adjusted HR = 0.42, p = 0.017). Exploratory analyses suggested elevated FGA in PD-L1-high tumors and a trend toward prolonged PFS after adjusting for PD-L1 status, though these findings require validation in larger cohorts. Multiplex immunofluorescence revealed significantly higher densities of CD4⁺, CD8⁺, and CD16a⁺ cells in FGA‑high regions (all p < 0.01). Two distinct spatial patterns were identified in both LUSC and LUAD. Pattern I featured direct immune cell infiltration into FGA-enriched regions with closer immune-tumor contact ( p < 0.01), whereas Pattern II demonstrated immune concentration within FGA-outlined tumor nests with predominant accumulation on the tumor side. Transcriptomic analysis revealed that FGA exposure was associated with immune activation in both LUSC and LUAD cell lines and additional metabolic reprogramming in LUAD cell lines. Immunohistochemical assessment of FGA represents a clinically practical biomarker associated with improved outcomes in ICI-treated NSCLC. Preliminary mechanistic exploration suggests that FGA is associated with an immunologically active but histology-dependent tumor microenvironment.