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The quest for high confidence mutations in plasma: searching for a needle in a haystack

Next generation sequencing of circulating tumor DNA (ctDNA) from patient plasma is becoming more widespread in oncology clinical trials. The noninvasive nature of acquiring these samples is particularly important when resection of representative tumor samples is not advised or not possible. However, profiling of ctDNA has challenges to overcome, such as low concentration of ctDNA shed from the tumor and a low signal:noise ratio caused by somatic alterations with less than 1% variant allele fraction. Improving the sensitivity of these assays to detect low allele frequency events with high confidence requires robust sequencing of low input libraries while employing error correction to reduce background noise. To overcome these challenges, we have incorporated unique molecular identifiers (UMIs) into our NGS workflow. Using these novel adapters paired with our proprietary bioinformatics pipeline (AstraZeneca), the number of false positive variants reported for allele fractions less than 0.5% was reduced tenfold. We also refined our curation based on the mapping quality and strand bias in the vicinity of each variant to further reduce the background noise. In this webinar we discuss our current NGS ctDNA workflow and our future plans to increase our sequencing sensitivity with these novel UMI adapters.

Published on: April 26, 2018