Genomic features of metastatic testicular sex cord stromal tumors.

532Background: 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 e...