Cell-Free DNA as a Diagnostic Blood-Based Biomarker for Colorectal Cancer: A Systematic Review.

Background: Circulating tumour DNA (ctDNA) has emerged as an excellent candidate for the future of liquid biopsies for many cancers. There has been growing interest in blood-based liquid biopsy because of the potential of ctDNA to produce a noninvasive test that can be used for: the diagnosis of colorectal cancer, monitoring therapy response, and providing information on overall prognosis. The aim of this review was to collate and explore the current evidence regarding ctDNA as a screening tool for colorectal cancer (CRC).
Methods: A systematic review of published articles in English over the past 20 y was performed using Medline, Embase, and Cochrane databases on May 23, 2017. After a full-text review, a total of 69 studies were included. Two assessment tools were used to review and compare the methodological quality of these studies.
Results: Among the 69 studies included, 17 studies reviewed total cfDNA, whereas six studies looked at the DNA integrity index and 15 focused on ctDNA. There were a total of 40 studies that reviewed methylated cfDNA with 19 of these focussing specifically on SEPT9.
Conclusions: The results of this review indicate that methylated epigenetic ctDNA markers are perhaps the most promising candidates for a blood-based CRC-screening modality using cell-free (cf) DNA. Methylated cfDNA appears to be less specific for CRC compared to ctDNA; however, they have demonstrated good sensitivity for early-stage CRC. Further research is required to determine which methylated cfDNA markers are the most accurate when applied to large cohorts of patients. In addition, reliable comparison of results across multiple studies would benefit from standardization of methodology for DNA extraction and PCR techniques in the future.
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