Circulating exosomal microRNA-4497 as a potential biomarker for metastasis and prognosis in non-small-cell lung cancer

Circulating exosomal microRNAs (miRNAs) have shown great potential for the diagnosis, prognosis, and treatment monitoring of patients with non-small-cell lung cancer (NSCLC). Our main purpose was to determine the clinical value of serum exosomal miR-4497 as a new non-invasive biomarker for NSCLC. The exoRNeasy Kit (QIAGEN, Hilden, Germany) was used to isolate exosomes and exoRNA from the serum of 84 patients with NSCLC (NSCLC group), 30 patients with benign lung lesion (BLL group), and 47 healthy controls. Six serum exosomal miRNAs (Let-7b-5p, miR-122-5p, miR-155-5p, miR-223-3p, miR-320c, and miR-4497) were selected as candidate miRNAs and analyzed using real-time qPCR, among which miR-4497 displayed the most striking differences. Exosomal miR-4497 expressed significantly lower in NSCLC than in BLL patients and healthy controls ( P < 0.001). Further investigation showed that miR-4497 was negatively correlated with the malignant characteristics of tumors (tumor size, tumor–node–metastasis [TNM] stage, and distant metastasis) and was an independent tumor suppressor ( P < 0.05). According to receiver operating characteristic (ROC) analysis, exosomal miR-4497 independently exhibited excellent diagnostic efficacy, which could be improved by combining it with traditional markers (for identifying tumor size, the area under the curve [AUC] = 0.761; TNM stage, AUC = 0.878; distant metastasis, AUC = 0.895; all P < 0.001). Moreover, longitudinal analysis revealed that exosomal miR-4497 levels increased after chemoradiotherapy ( P < 0.001). According to the survival analysis, poor overall survival (OS) and disease-free survival (DFS) were associated with low exosomal miR-4497 levels ( P < 0.05). Moreover, exosomal miR-4497 was an independent protective factor affecting DFS (hazard ratio = 0.190, P = 0.009) in the Cox proportional hazards model. Therefore, serum exosomal miR-4497 can be used as a potential biomarker to identify NSCLC and healthy individuals or BLL patients for early screening or as a biomarker for staging and grading, prognosis, and monitoring recurrence, metastasis, and the therapeutic effects in patients with NSCLC.