Background: Current serum tumor markers (STMs) for testicular germ cell tumor (GCT) are limited by low sensitivity. Growing evidence supports the use of circulating miR-371a-3p as a superior marker for malignant (viable) GCT management. We evaluated the real-world application of serum miR-371a-3p levels in detecting viable GCT among patients undergoing partial or radical orchiectomy. Methods: Serum samples were collected from 69 consecutive patients pre-orchiectomy. Performance characteristics of serum miR-371a-3p were compared with conventional STMs (AFP/β-hCG/LDH) between viable GCT patients and those without viable GCT on orchiectomy pathology. Relative miR-371a-3p levels were correlated with clinical course. Kruskal-Wallis test and linear and ordinal regression models were used for analysis. Results: For detecting viable GCT, combined conventional STMs had a specificity of 100%, sensitivity of 58%, and area under the curve (AUC) of 0.79 (Table). The miR-371a-3p test showed a specificity of 100%, sensitivity of 93%, and AUC of 0.978. Median relative expression of miR-371a-3p in viable GCT patients was >6,800-fold higher than in patients lacking viable GCT. MiR-371a-3p levels correlated with composite stage (CS) (p=0.006), and, among CS I patients, independently associated with embryonal carcinoma percentage (p=0.0012) and tumor diameter (p<0.0001). Six patients received orchiectomy after chemotherapy and were correctly predicted to have presence or absence of viable GCT by the miR-371a-3p test. Conclusions: If validated, the miR-371a-3p test can be used in conjunction with conventional STMs to aid clinical decision-making. A positive miR-371a-3p test in patients after preoperative chemotherapy or with solitary testes could potentially guide subsequent orchiectomy or observation.

NPV - Negative Predictive Value, PPV – Positive Predictive Value, NL – upper normal limit used in diagnosis.