MicroRNA-371a-3p Represents a Novel and Effective Diagnostic Marker for Testicular Germ Cell Tumours: A Real-World Prospective Comparison with Conventional Approaches.

Background/Objectives: Testicular germ cell tumours (GCT) have high cure rates, especially in early stages. MicroRNA-371a-3p (M371) has recently emerged as a highly sensitive biomarker for malignant GCTs, except teratoma. This study aimed to evaluate the diagnostic performance of M371-test in a real-life clinical setting, compared to conventional markers alpha-fetoprotein (AFP), lactate-dehydrogenase (LDH), and beta-human chorionic gonadotropin (β-HCG) in patients with suspected GCT. Methods: The study, approved by the Ethic-Committee of the Provincial Hospital of Bolzano (N.97-2021), included 91 M371-tests, performed from March 2021 to May 2025. A total of 75 patients had suspected GCT; 19 healthy males served as control. Serum levels of M371, AFP, LDH, and β-HCG were compared with final histopathological diagnosis. M371 was also assessed in controls to evaluate test performance. Secondary analyses investigated correlations between preoperative M371 levels and tumour size in non-metastatic patients, and between M371-levels and clinical stage in the entire GCT cohort. A cut-off of RQ > 5 (relative quantification) was used to calculate sensitivity, specificity, and predictive values. Results: M371 showed a sensitivity of 90.9% and specificity of 89.3%, outperforming in terms of sensitivity AFP (20.4%/96.4%), LDH (40.9%/96.4%), and β-HCG (43.1%/100%). Positive predictive value (PPV) and negative predictive value (NPV) were 93.0% and 86.2%, respectively. Sensitivity was 95% for non-seminomas and 87.5% for seminomas. In non-metastatic patients, M371 levels correlated with tumour size and were significantly higher in advanced stages (median RQ 1128.35 vs. 98.36; p = 0.015). Conclusions: M371 showed excellent diagnostic performance, even for small tumours, supporting its clinical use. Further studies are needed to define its role in treatment planning and follow-up.