Integrated Analysis of Ovarian Juvenile Granulosa Cell Tumors Reveals Distinct Epigenetic Signatures and Recurrent TERT Rearrangements

Purpose: Adult granulosa cell tumor (AGCT) is character-ized by the somatic FOXL2 p.C134W mutation, and recur-rences have been associated with TERT promoter and KMT2D- truncating mutations. Conversely, the molecular underpinnings of the rare juvenile granulosa cell tumor (JGCT) have not been well elucidated. To this end, we applied a tumor-only inte-grated approach to investigate the genomic, transcriptomic, and epigenomic landscape of 31 JGCTs to identify putative oncogenic drivers. Experimental Design: Multipronged analyses of 31 JGCTs were performed utilizing a clinically validated next-generation sequenc-ing (NGS) panel targeting 580 cancer-related genes for genomic interrogation, in addition to targeted RNA NGS for transcriptomic exploration. Genome-wide DNA methylation profiling was con-ducted using an Infinium Methylation EPIC array targeting 866,562 CpG methylation sites. Results: We identified frequent KMT2C-truncating mutations along with other mutated genes implicated in the switch/sucrose nonfermentable (SWI/SNF) chromatin remodeling complex, in addition to previously reported hotspot AKT1 and DICER1 muta-tions. Targeted transcriptome sequencing revealed recurrent TERT rearrangements (13%) involving partners CLPTM1L or DROSHA, and differential gene expression analysis showedFGFR1 upregulation in the TERT non-rearranged JGCTs under direct promoter control. Genome-wide DNA methylation rendered a clear delineation between AGCTs and JGCTs at the epigenomic level, further support -ing its diagnostic utility in distinguishing among these tumors. Conclusions: This is the largest comprehensive molecular study of JGCTs, where we further expand our current understanding of JGCT pathogenesis and demonstrate putative oncogenic drivers and TERT rearrangements in a subset of tumors. Our findings further offer insights into possible targeted therapies in a rare entity.