Abstract LB-223: Whole genome sequencing of rhabdomyosarcoma germline cohort identifies low frequency of pathogenic mutations

Abstract Introduction: Rhabdomyosarcoma (RMS) is among the most frequently occurring tumors in Li-Fraumeni syndrome patients and is often observed in patients with a strong family history of cancer. Recent studies suggest that at least 10% of children with cancer harbor an underlying pathogenic germline mutation, although the frequency in children with RMS is not well characterized. In this study we sought to determine the rate of likely pathogenic germline mutations in rhabdomyosarcoma patients, unselected for family history. Methods: Of 275 RMS patients enrolled on one clinical trial (COG ARST0531), whole-genome sequencing was performed on blood-derived DNA of an initial set of 50 using the Illumina HiseqX to an average sequencing depth of 44.9X [34.2-58.4]. Single nucleotide variants (SNVs) and Indels were called and filtered to select only those occurring in exons or splicing regions. Variants were further filtered to include only those with a frequency of <0.5% in the ExAC database and lying in one of 99 genes identified as a cancer predisposition gene in the COSMIC Cancer Gene census. Nonsynonymous SNVs were required to be predicted as deleterious by one or more of Polyphen, mutation assessor or sift. Results: Across the 50 initial samples, a total of 290 variants ([0-17], median of 5) passed the described filters. Notably, no point mutations were identified in TP53 in the initial 50 samples. Two samples contained variants annotated as pathogenic in ClinVar - a frameshift deletion in CHEK2 and a rare SNP in MUTYH. Also notable was a potentially pathogenic frameshift deletion in MSH6 that lacked previous annotation. Conclusions: Our preliminary analysis suggests a lower incidence of causative TP53 mutations in RMS than previously suggested. Whole genome sequencing of the remaining samples in the cohort along with analysis of copy number and structural variants is ongoing. Statistical analysis of the entire cohort of 275 patient samples will allow for the most complete characterization of the germline genomic landscape of rhabdomyosarcoma to date. This information will better inform clinical surveillance and management parameters for RMS patients and families. Citation Format: Nicholas Light, Philip Lupo, Javed Khan, Joshua Schiffman, Douglas Hawkins, Adam Shlien, David Malkin. Whole genome sequencing of rhabdomyosarcoma germline cohort identifies low frequency of pathogenic mutations [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr LB-223. doi:10.1158/1538-7445.AM2017-LB-223

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