Circulating MicroRNAs in Testicular Germ Cell Tumors: Biomarkers for Diagnosis, Surveillance, and Treatment Stratification.

Testicular germ cell tumors (TGCTs) are highly curable malignancies, yet their clinical management still relies heavily on conventional serum tumor markers, including alpha-fetoprotein, beta-human chorionic gonadotropin, and lactate dehydrogenase, which have limited sensitivity and specificity in several clinically relevant settings. Circulating microRNAs, particularly miR-371a-3p, have emerged as promising liquid biopsy biomarkers with potential applications across the TGCT disease continuum. This narrative review summarizes the current evidence on the biological basis, diagnostic performance, clinical utility, and limitations of circulating microRNAs in TGCTs. MiR-371a-3p demonstrates high diagnostic accuracy for viable non-teratomatous TGCTs and consistently outperforms classical serum tumor markers in primary diagnosis. Its rapid decline after effective treatment and its association with tumor burden support potential roles in chemotherapy monitoring, early relapse detection during surveillance, and the assessment of selected post-chemotherapy residual masses. However, its inability to detect teratoma remains a major biological limitation, particularly in non-seminomatous residual disease and surveillance settings. Additional barriers to implementation include assay heterogeneity, the lack of universally accepted cutoffs, the variable use of serum versus plasma, and the absence of broad regulatory approval. Emerging translational data suggest that miR-371a-3p may also contribute to tumor-microenvironment communication and cisplatin resistance, although these findings remain preclinical. Overall, miR-371a-3p represents one of the most promising biomarkers in TGCT management, but its routine clinical integration will require standardized analytical protocols and prospective validation in marker-guided decision pathways.