RARE-07. THE LANDSCAPE OF GENOMIC ALTERATIONS IN ADAMANTINOMATOUS CRANIOPHARYNGIOMAS

INTRODUCTION: Adamantinomatous craniopharyngiomas (ACPs) are characterized by activating mutations in the CTNNB1 gene. Here we perform a comprehensive genomic analysis of 23 ACPs to define the landscape of genomic alterations in this disease. METHODS: We performed whole-genome sequencing of 24 ACPs and their matched normal tissues. We used Mutect 2.0 to detect mutations and indels in these samples and MutSig2CV to identify significant mutations. Copy numbers were called using the GATK4 pipeline and GISTIC 2.0 was applied to identify significant alterations. Finally, SvABA was applied to identify genome-wide structural variants and rearrangements. RESULTS: 18/24 (75%) of the sequenced ACPs harbored activating mutations in exon 3 of CTNNB1 gene with an average variant allele fraction (VAF) of 0.4±0.1. These mutations have previously been shown to activate the WNT signaling pathway in these tumors. No other significantly recurrent mutations were detected in our samples. The ACPs were quiet with regard to copy number alterations and no recurrent amplifications or deletions were detected. 528 structural variations and rearrangements were detected in total in all 24 samples with an average of 22 variants per sample. Gene-Set Enrichment Analysis (GSEA) of the RNAseq data revealed upregulation of WNT/B-catenin (FDR q-value <0.25) in the CTNNB1 mutant samples compared to CTNNB1 WT samples. CONCLUSION: Our study identified previously described activating CTNNB1 mutations in the majority of ACPs. In addition, we identified several rearrangements and structural variations in these tumors that could play an important role in the pathogenesis of the disease.