In Situ Expression of miR-371a-3p and miR-373-3p in Testicular Germ Cell Tumours and Detection in Serum

BACKGROUND: Testicular germ cell tumours (TGCTs) are the most common type of tumour diagnosed in young men, and reliable non-invasive biomarkers are crucial for clinical management. MicroRNAs (miRNAs) from the miR-371-373 cluster have recently been identified as novel and more sensitive serum biomarkers than the conventional protein-based markers. However, few studies have looked at the expression of the miR-371-373 cluster in tumour tissue.

OBJECTIVES: To investigate the expression of miR-371a-3p and miR-373-3p in testicular tumour tissue and compare it with matched serum levels.

MATERIALS AND METHODS: We used single-molecule in situ hybridisation (smISH) on tumour tissue from 33 patients-30 with TGCT and three with the precursor lesion, germ cell neoplasia in situ (GCNIS)-of whom 20 had paired pre-orchiectomy serum samples. We validated the smISH using RT-qPCR on tumour tissue from 12 patients.

RESULTS: Both miR-371a-3p and miR-373-3p were positive in all tumour tissue samples except for teratoma. Also, patients with TGCT that were negative in serum for either miR-371a-3p (n = 4) or miR-373-3p (n = 6) showed positive expression in their tumour tissue. The expression levels varied across tumours, with miR-373-3p generally showing higher expression than miR-371a-3p. All samples with GCNIS were positive, both when adjacent to tumour tissue (n = 6) and without an invasive component (n = 3).

DISCUSSION: Although our study only included 33 cases, we covered all TGCT components. In situ expression patterns indicate that miR-373-3p has a diagnostic value independent of miR-371a-3p.

CONCLUSION: All non-teratomatous TGCT and GCNIS tissue showed expression of miR-371a-3p and miR-373-3p, and the lack of detection in serum consequently seems to be related to technical sensitivity.