Circulating tumour DNA in colorectal cancer: current and emerging clinical applications

Circulating tumour DNA (ctDNA), often referred to as liquid biopsy, is a promising, minimally invasive biomarker in both early-stage and metastatic colorectal cancer (CRC). In early-stage CRC, ctDNA allows the detection of minimal residual disease (MRD) after curative-intent surgery, enabling the identification of patients at higher risk of recurrence and potentially guiding adjuvant therapy decisions. Serial analysis of ctDNA can be performed to assess the efficacy of adjuvant chemotherapy by providing an early molecular read-out of treatment response, and during surveillance to detect molecular recurrence prior to radiological or clinical relapse. In the advanced setting, ctDNA holds promise as a minimally invasive method of detecting emerging resistance mutations and monitoring response to therapy over time. This review highlights the current landscape of evidence, the evolving clinical applications and limitations of ctDNA in colorectal cancer.