Expression of ENPP1 in Testicular Germ Cell Tumors: Exploring Its Role in the Pathobiology of Distinct Histotypes and in Prognosis.

INTRODUCTION

Testicular germ cell tumors (TGCTs) are the most common solid malignancies among young men. Despite good response to cisplatin-based chemotherapy, side effects negatively affect quality of life. Recent development of ecto-nucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1) inhibitors opens opportunity for targeted therapy, but ENPP1 expression in TGCTs has not been characterized. We aimed to assess ENPP1 immunoexpression in a cohort of primary and metastatic TGCTs, and in normal testicular parenchyma, looking into differential immunoexpression patterns among subtypes and clinicopathological correlations.

METHODS

Overall, 90 TGCT individual tumor components from 63 patients diagnosed and treated at a comprehensive cancer center were assessed, using immunohistochemistry to ascertain biomarker expression (combined score of stained tumor cells percentage and intensity). In silico analysis of The Cancer Genome Atlas (TCGA) and Human Protein Atlas (HPA) datasets was performed for additional validation.

RESULTS

Significant differences in ENPP1 expression across TGCT subtypes were disclosed. Seminomas and embryonal carcinomas (ECs) showed significantly higher ENPP1 expression compared to other subtypes, the highest levels being found in EC, which was confirmed with in silico analysis of TCGA and HPA. Expression in metastatic samples was overall lower compared to primary TGCTs. ENPP1 was not expressed in germ cells of healthy testicular parenchyma.

CONCLUSION

We demonstrate that ENPP1 is expressed in TGCTs, mostly EC (a frequently aggressive tumor subtype), followed by seminoma (the most common TGCT subtype), suggesting potential responsiveness to novel ENPP1 inhibitors. Absent expression in germ cells of healthy testicular parenchyma suggest cancer cells specificity and low probability of fertility-related toxicity.