Background:

Metastatic Leydig cells tumors (LCT) are rare, difficult to treat malignancies without known underlying molecular-genetic events. An index case of testicular metastatic LCT showed LDLR-TERT gene fusion upon routine genetic profiling for detection of therapeutic targets, which was then followed by an investigation into a cohort of additional LCT

Methods:

21 testicular LCT (7 metastatic and 14 primary tumors) from 3 participating institutions (Caris Life Sciences, Phoenix ,USA; Clinical Hospital Centre Sestre Milosrdnice, Zagreb, Croatia and Biopticka Laborator, Plzen, Czech Republic) were analyzed using massively parallel DNA and RNA sequencing (NGS); Immunohistochemistry (IHC) was used for detection of expression of selected protein biomarkers (PD-L1, androgen receptor (AR), ARv7, Topo1a).

Results:

TERT gene fusions were detected only in metastatic Leydig cell tumors, in three of 5 successfully analyzed cases (RMST:TERT, LDLR:TERT and B4GALT5:TERT, respectively). The case with B4GALT5:TERT fusion also showed amplifications (>6 copies) of TOP1 and CCND3 genes. TP53 mutation (M246I) was detected in one metastatic tumor without TERT fusion. No gene fusions were found in any primary tumors (0/8 successfully analyzed). 4/7 primary tumors showed multiple gene amplifications, without a consistent pattern. At the protein level (IHC) 5/7 metastatic and 6/7 primary tumors over-expressed TOP1. Full length AR was overexpressed in 7/8 primary tumors (without detectable ARv7 mRNA or ARv7 protein), but only in 1 of 5 metastatic LCT. No tumors exhibited high tumor mutational burden, microsatellite instability nor expressed PD-L1 in tumor cells.

Conclusions:

: Our study for the first time identified TERT gene fusions as a main/sole detected genetic alteration and a potential therapeutic target in malignant, metastatic Leydig cell tumors. Additional biomarkers (TOP1 amplification and over-expression) may help guide decisions on chemotherapy for selected individual patients. Androgen receptor blockade may be considered in AR overexpressing tumors without evidence of ARv7 presence