MicroRNA (miRNA) in bronchoalveolar lavage (BAL) for lung cancer: a systematic review

Background Lung cancer remains one of the most lethal malignancies globally, with a five-year survival rate of approximately 23% largely due to diagnosis at advanced stages. As tissue biopsy presents challenges related to accessibility, invasiveness, and procedural risks, there is a growing need for minimally invasive diagnostic alternatives. This systematic review evaluates the diagnostic and prognostic value of microRNAs (miRNAs) derived from bronchoalveolar lavage (BAL) fluid as potential non-invasive biomarkers for lung cancer detection and subtype differentiation. Methods A structured literature search was conducted in accordance with PRISMA 2020 guidelines across ScienceDirect, PubMed, and Scopus, yielding 11 eligible studies published between 1 January 2015 until 6 December 2025. Results Several BAL-derived miRNAs, including miR-19, miR-21, miR-29a, miR-126, miR-10b, and miR-30a, were consistently reported as differentially expressed in lung cancer patients compared with control groups. Reported diagnostic performance varied across studies, with area under the curve values ranging from 0.675 to 0.997 and sensitivities reaching up to 95%. Additional findings indicated that miRNAs such as miR-1246b and miR-21 were associated with tumor presence, disease progression, immune regulation, and epithelial–mesenchymal transition. Conclusion Overall, the evidence suggests that BAL-derived miRNAs hold considerable potential as liquid biopsy biomarkers for early detection, prognostic assessment, and treatment stratification in lung cancer. Nevertheless, further multicenter validation and methodological standardization are required before these biomarkers can be integrated into routine clinical practice.