Circulating Tumour DNA to Guide Treatment of Gastrointestinal Malignancies

Background: Gastrointestinal cancers are among the most common cancers worldwide and account for a high proportion of cancer-related mortality. Advancements to improve outcomes are constrained by the lack of biomarkers that can offer early diagnostic and prognostic information as traditional serological tumour markers and conventional imaging approaches are not able to provide early information regarding disease recurrence and treatment outcomes. Recent advances in technology have allowed the detection of circulating tumour DNA (ctDNA) in plasma, nucleic acid fragments released into the circulation from primary or metastatic lesions undergoing apoptosis and necrosis. A growing body of evidence has emerged supporting the use of ctDNA in many aspects of cancer care. Summary: This review focuses on the potential role of ctDNA in the management of patients with gastrointestinal cancers including colorectal, pancreatic, and upper gastrointestinal cancers. In this review, we discuss its possible utility in screening, detection of minimal residual disease and prognostication, longitudinal surveillance, and identification of therapeutic targets and resistance incorporating recent literature and ongoing randomised clinical trials. Key Messages: ctDNA has substantial potential as a clinically useful marker in the management of gastrointestinal cancers from cancer screening through to treatment of advanced disease.