GENOMIC CHARACTERIZATION OF ADULT-TYPE GRANULOSA CELL TUMORS: IMPLICATIONS FOR PATHOGENESIS AND TREATMENT OF RECURRENT DISEASE

BACKGROUND: Adult granulosa cell tumors (AGCT) represent 3-5% of all ovarian cancers. These tumors are characterized by their slow growth and usually occur in postmenopausal women with a median age of diagnosis of 50 to 54 years. The majority of patients are diagnosed as stage I and are treated with surgery to remove their ovaries and uterus. Although these treatments are effective at first, one third of patients relapse leading to mortality in 50-80% of relapsed patients. The best course of treatment for patients with recurrent advanced stage disease is optimal debulking surgery. Currently, there are no effective treatments available for patients where surgery is not an option. Our research team previously discovered a somatic missense mutation (c.402C\u003eG; pC134W) in the transcription factor Forkhead box L2 (FOXL2) in 97% of AGCTs. We also discovered frequent activating telomerase reverse transcriptase (TERT) promoter mutations in AGCT. As the FOXL2 C134W mutation is present in essentially all AGCTs and telomerase reactivation is required for tumorigenesis, it is likely that additional mutations are responsible for the variability in clinical behaviour. This study aims to describe the mutational landscape of AGCT to further refine our understanding of the frequent recurrence of this disease. METHODS: Using whole genome sequencing (WGS), we characterized the genomes of ten AGCTs and their matched normal blood. We observed that AGCTs have a low mutation burden and the majority of mutations are single nucleotides variants. We have collected 516 formalin-fixed paraffin-embedded AGCT specimens including primary, recurrent and metastatic tumors from seven international centres for validation of our WGS results. Allelic discrimination assays were used for hotspots mutations, in addition to targeted sequencing of 39 genes of interest using a custom amplicon-based panel in our extension cohort. RESULTS: Of the 39 genes analyzed, the third most commonly mutated gene (FOXL2 and TERT being the first and second most common) in our preliminary analysis of 88 cases was lysine (K)-specific methyltransferase 2D (KMT2D or MLL2). We identified various missense and nonsense mutations in this gene in 16 of 88 AGCTs (18%) analyzed thus far. KMT2D is a histone methyltransferase that targets histone H3 lysine 4 (H3K4), a methylation activation mark, and has an essential role in transcriptional regulation. Using an allelic discrimination assay, we identified a known hotspot mutation (c.49G\u003eA;p.E17K) in v-akt murine thymoma viral oncogene 1 (AKT1) in 2 of 67 (3%) AGCT patients, one of which the mutation was present in all three recurrent specimens from the same patient. AKT1 E17K mutation has been reported in multiple cancers such as breast, colorectal and high grade serous ovarian cancer at a low prevalence. A recent clinical trial of AKT inhibition in solid tumors with AKT1 mutations included one recurrent AGCT patient and showed significant tumor regression in one metastatic site. CONCLUSION:AKT1 E17K mutations are present in AGCT at a low prevalence and could represent a therapeutic target for patients with recurrent advanced stage disease harbouring this mutation. Citation Format: Jessica A. Pilsworth, Dawn R. Cochrane, Samantha Neilson, Anniina E.M. Farkkila, Hugo M. Horlings, Satoshi Yanagida, Janine Senz, Yi Kan Wang, Bahar Moussavi, Daniel Lai, Ali Bashashati, Jacqueline Keul, Adele Wong, Hannah van Meurs, Sara Y. Brucker, Florin-Andrei Taran, Bernhard Kramer, Annette Staebler, Esther Oliva, Sohrab P. Shah, Stefan Kommoss, Friedrich Kommoss, C. Blake Gilks and David G. Huntsman. GENOMIC CHARACTERIZATION OF ADULT-TYPE GRANULOSA CELL TUMORS: IMPLICATIONS FOR PATHOGENESIS AND TREATMENT OF RECURRENT DISEASE [abstract]. In: Proceedings of the 12th Biennial Ovarian Cancer Research Symposium; Sep 13-15, 2018; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2019;25(22 Suppl):Abstract nr GMM-047.