Circulating tumour cells and DNA as liquid biopsies in gastrointestinal cancer.

Background: Blood is the most extensively studied body fluid and, because it contains circulating tumour cells (CTCs) and circulating tumour-derived cell-free DNA (ctDNA), it may represent a liquid biopsy for cancer. Methods for enrichment and detection of CTCs and ctDNA, their clinical applications and future opportunities in gastrointestinal cancers were the focus of this review.

Methods: The PubMed database was searched for literature up to 24 June 2017, with a focus on the past 10 years. Identified articles were further scrutinized for relevant references. Articles were those in English relating to colorectal, gastric and pancreatic cancer.

Results: Both CTCs and ctDNA are in low abundance compared with other cellular components of blood, but effective enrichment and highly sensitive techniques are available for their detection. Potential clinical applications of these liquid biopsies include screening, prognostic stratification, therapy administration, monitoring of treatment effect or resistance, and surveillance. Liquid biopsies provide opportunities to reduce the need for invasive tissue sampling, especially in the context of intratumoral heterogeneity and the need for tumour genotyping.

Conclusion: Liquid biopsies have applications in gastrointestinal cancers to improve clinical decision-making.