Genomic features of metastatic testicular sex cord stromal tumors.

Abstract

532 Background: Metastatic testicular sex cord stromal tumors of the testis (MSCST) comprise an extremely uncommon form of genitourinary malignancy. In a comparative genomic study, we performed comprehensive genomic profiling (CGP) to characterize the genomic alterations (GA) in MSCST and to enable the search for potential therapy targets. Methods: The MSCST were classified as metastatic Leydig Cell Tumors (LCT), Sertoli Cell Tumors (SCT) and Undifferentiated (USCST). In this study, 10 cases of LCT, 6 cases of SCT and 3 cases of USCST underwent hybrid-capture based CGP to evaluate all classes of genomic alterations. Tumor mutational burden (TMB) was determined on 1.1 Mbp of sequenced DNA and microsatellite instability (MSI) was determined on 114 loci. Results: All patients had clinically advanced recurrent and/or metastatic disease. The primary testis tumor was used for sequencing in 6 MSCST (32%) and a metastatic site in 9 (68%) of the MSCST. In 10 (91%) of 11 MSCST positively stained by IHC for inhibin expression. The overall frequencies of GA were similar in all LCT, SCT and UTST ranging from 3.0 to 3.5 GA/tumor. The most frequent untargetable GA found in all MSCST cases included CTNNB1 and CDKN2A/B, both ranging from 20-33% of cases. Targetable GA were uncommon in all MSCST sub-groups but several tumors featured potential for cell cycle inhibitors ( CDK4 in LCT), MTOR inhibitors ( RICTOR, NF2 and PTEN in all 3 tumor types), hedgehog inhibitors ( PTCH1 in LCT) and PARP inhibitors ( BAP1 in SCT). No MSI-High status was identified in any MSCST. The TMB was also low in all MSCST groups. Conclusions: Although the 3 subgroups of testicular MSCST feature defining histopathologic features, these tumors have similar genomic signatures on CGP. The low levels of GA per tumor, infrequent tumor aneuploidy, absence of MSI-High status and low TMB all indicate that testicular MSCST are genetically stable. However, rare cases of testicular MSCST reveal GA linked to potential targeted therapy benefits on CGP linked to dysregulation of multiple biologic pathways. In contrast, the lack of MSI-High status and overall low TMB in testicular MSCST indicates a likely lack of benefit for immunotherapies for these rare forms of malignancy.