A Review of Circulating Tumor DNA (ctDNA) and the Liquid Biopsy in Cancer Diagnosis, Screening, and Monitoring Treatment Response.

The concept of liquid biopsy is based on the knowledge that blood or secretions from the body contain tumor cells, nucleic acids, cellular components, and tumor metabolites. Detection of circulating DNA (ctDNA) in liquid biopsy material shows the most promise due to the advances in DNA technologies that have made detection and sample screening possible. Clinical trials have begun to evaluate ctDNA monitoring for response to cancer treatment in clinical settings for non-small cell lung cancer (NSCLC), breast cancer, and colorectal cancer (CRC). However, most liquid biopsy tests introduced into the clinic have only been able to identify one or two features of tumor DNA, which limits the specificity of the test. In early 2025, a study led by a research team at Oxford University identified a new blood test, TriOx, developed using machine learning to detect multiple types of cancer at an early stage. These new blood tests may revolutionize oncology and make early cancer detection as routine as other diagnostic blood tests, such as blood glucose testing. This article aims to review ctDNA and liquid biopsy in the diagnosis, early detection, and monitoring of treatment response in cancer.