Diagnostic and Prognostic Roles of Blood-Based Immune Biomarkers in Non-Small Cell Lung Cancer: An Umbrella Review of Systematic Reviews and Meta-Analyses.

Blood-based biomarkers have emerged as promising, minimally invasive tools for the diagnosis, prognostic stratification, and treatment monitoring of non-small cell lung cancer (NSCLC), including markers of tumor burden, tumor dissemination, immune signaling, and post-transcriptional regulation. However, evidence across biomarker classes remains fragmented. This study aimed to synthesize published evidence on major blood-based biomarkers relevant to diagnosis, prognosis, treatment stratification, and monitoring in NSCLC. PubMed was searched for systematic reviews and meta-analyses of blood-based biomarkers in NSCLC. Of 356 screened records, 82 underwent full-text review, and 57 systematic reviews/meta-analyses were included. Biomarkers were grouped into four categories: circulating tumor DNA (ctDNA), circulating tumor cells (CTCs), cytokines/soluble immune proteins, and non-coding RNAs (ncRNAs). Reported pooled effect estimates were extracted by biomarker class and evidence domain, and the methodological quality of included reviews was assessed using AMSTAR 2. Evidence was unevenly distributed across biomarker classes and evidence domains. Circulating ncRNAs were mainly represented in diagnostic and prognostic evidence; selected diagnostic ncRNAs, including miR-145, miR-25, and circRNAs, showed reported AUCs ranging from 0.83 to 0.85. ctDNA was represented across diagnostic, prognostic, treatment-stratification, and dynamic monitoring evidence, with ctDNA positivity associated with poorer survival or recurrence outcomes and ctDNA clearance or decline associated with improved outcomes. CTC evidence was primarily prognostic, with CTC positivity associated with worse overall survival and disease-free survival. Soluble immune biomarker evidence was also primarily prognostic, with elevated soluble PD-L1 and IL-6 associated with adverse survival outcomes and limited exploratory monitoring evidence for exosomal PD-L1. Overall, the evidence suggested distinct but complementary roles across biomarker classes, although direct head-to-head comparisons were lacking. Blood-based biomarkers show potential to support diagnosis, prognosis, and longitudinal monitoring in NSCLC, but their reported utility differs by biomarker class and clinical context. In the available review-level evidence, ncRNAs were mainly represented in diagnostic and prognostic evidence, while ctDNA was represented across diagnostic, prognostic, treatment-stratification, and dynamic monitoring evidence. CTCs were mainly represented in prognostic evidence, and soluble immune biomarkers were primarily represented in prognostic evidence, with limited exploratory evidence for dynamic monitoring. Further assay standardization, prospective validation, and direct comparative studies are needed before these biomarkers can be routinely integrated into clinical practice.