Paired tumor and normal whole genome sequencing of metastatic olfactory neuroblastoma

Abstract

Background: Olfactory neuroblastoma (ONB) is a rare cancer of the sinonasal tract with little molecular characterization. We performed whole genome sequencing (WGS) on paired normal and tumor DNA from a patient with metastatic-ONB to identify the somatic alterations that might be drivers of tumorigenesis and/or metastatic progression.

Methodology/principal findings: Genomic DNA was isolated from fresh frozen tissue from a metastatic lesion and whole blood, followed by WGS at >30X depth, alignment and mapping, and mutation analyses. Sanger sequencing was used to confirm selected mutations. Sixty-two somatic short nucleotide variants (SNVs) and five deletions were identified inside coding regions, each causing a non-synonymous DNA sequence change. We selected seven SNVs and validated them by Sanger sequencing. In the metastatic ONB samples collected several months prior to WGS, all seven mutations were present. However, in the original surgical resection specimen (prior to evidence of metastatic disease), mutations in KDR, MYC, SIN3B, and NLRC4 genes were not present, suggesting that these were acquired with disease progression and/or as a result of post-treatment effects.

Conclusions/significance: This work provides insight into the evolution of ONB cancer cells and provides a window into the more complex factors, including tumor clonality and multiple driver mutations.

Figure 1. Circos plot for WGS results for ONB.

This figure depicts the genomic location in the outer ring and chromosomal copy number in the inner ring. The SNVs and indels are marked on the outer ring in their respective genomic locations. In the inner ring, copy gains are shown in red, while copy losses are shown in green. No interchromosomal translocations were observed by assessing counts of anomalous read pairs between specific regions of the genomes, noting that the use of shorter-paired end sequencing may limit our ability to detect these events with this analysis.

Figure 2. Differences between the germline and somatic sequences.

Details the statistics for the germline SNPs and somatic SNVs.