Abstract 2738: A commutable circulating tumor DNA (ctDNA) reference material

We developed and assessed a novel ctDNA reference material that was designed with an emphasis on commutability. Possessing qualities that are well-matched with clinical specimens is critical for a reference material, however many existing methods of preparing ctDNA analogues result in material that is not commutable for certain assays. For example, sonication of genomic DNA yields fragments across a broad range of sizes that must be used at greater input amounts relative to native cell-free DNA (cfDNA) - even after enzymatic end-repair to reduce damage. This can affect the utility of the reference material for assays that depend on the ligation of adapters to double-stranded DNA, such as many hybrid/capture-based Next Generation Sequencing (NGS) assays. If higher input amounts are not used, then the LOD and precision of such an assay may appear substantially poorer than expected. At the same time, sonicated DNA has been shown to be acceptable for amplicon-based ctDNA assays. We created commutable ctDNA reference material by starting with genomic DNA from GM24385 cells and mixing with synthetic variant-containing DNA sequences at defined ratios. The use of GM24385 cells allows for the comparison of detected variants against the NIST RM 8391 high confidence variants. The use of synthetic DNA permits addition of large numbers of different cancer-associated variants at defined allele frequencies. Fragmentation was followed by size-selection in order to obtain ctDNA-like sizes. Additional steps were performed to increase the amount of output material from the size-selection step. The general method of preparing the reference material is also compatible with native cfDNA, such as that isolated from cancer patients. The reference material was submitted to several testing laboratories along with similar sonicated material. When tested using hybrid/capture-based assays, variant detection was superior in the novel reference material compared to sonicated DNA when similar amounts of material were used as the input. We therefore conclude that our new reference material has greatly improved commutability compared to existing materials composed only of sonicated DNA. Citation Format: Yves Konigshofer, Farol L. Tomson, Matthew Ryder, Russell Garlick, Bharathi Anekella. A commutable circulating tumor DNA (ctDNA) reference material [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 2738. doi:10.1158/1538-7445.AM2017-2738