Correlation of Somatic Genomic Alterations Between Tissue Genomics and ctDNA Employing Next Generation Sequencing: Analysis of Lung and Gastrointestinal Cancers.

Next Generation Sequencing (NGS) of cancer tissues is increasingly being carried out to identify somatic genomic alterations that may guide physicians to make therapeutic decisions. However, a single tissue biopsy may not reflect complete genomic architecture due to the heterogeneous nature of tumors. Circulating tumor DNA (ctDNA) analysis is a robust noninvasive method to detect and monitor genomic alterations in blood in real time. We analyzed 28 matched tissue NGS and ctDNA from gastrointestinal and lung cancers for concordance of somatic genomic alterations, driver and actionable alterations. Six patients (21%) had at least one concordant mutation between tissue and ctDNA sequencing. At the gene level, among all the mutations (n=104) detected by tissue and blood sequencing 7.7% (n=8) of mutations were concordant. Tissue and ctDNA sequencing identified driver mutations in 60% and 64% of the tested samples, respectively. We found high discordance between tissue and ctDNA testing, especially with respect to the driver and actionable alterations. Both tissue and ctDNA NGS detected actionable alterations in 25 % of patients. When somatic alterations identified by each test were combined, the total number of patients with actionable mutations increased to 32 %. Our data show significant discordance between tissue NGS and ctDNA analysis. These results suggest tissue NGS and ctDNA NGS are complementary approaches rather than exclusive of each other. When performed in isolation, tissue and ctDNA NGS can each potentially miss driver and targetable alterations, suggesting that both approaches should be incorporated to enhance mutation detection rates. Larger prospective studies are needed to better clarify this emerging precision oncology landscape

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