Circulating tumor DNA testing and research in patients with gastrointestinal malignancies.

525Background: The hallmark of circulating tumor DNA (ctDNA) is its rapid turnaround and non-invasive nature. According to American Society of Clinical Oncology (ASCO) and College of American Pathologists joint ctDNA review published in March 2018, there is no sufficient evidence to support the use of ctDNA in practice for GI cancers. However, there were numerous studies presented at ASCO Annual Meeting supporting its value. We aimed to summarizing on its role in the management of gastrointestinal cancers based on the studies presented recently. Methods: We limited our search to keywords ‘ctDNA’, ‘circulating tumor DNA’, ‘cell-free DNA (cfDNA)’ and/or ‘liquid biopsy’, at the 2018 ASCO Annual Meeting library abstracts and presentations. Results: There were 35 studies that revolved around ctDNA as a diagnostic tool, prognostic marker and a measure of tumor heterogeneity in gastrointestinal cancers. Depending on the assay used, the results of several studies showed that ctDNA was able to identify relevant mu...