The persistent enigma of carcinoembryonic antigen in colorectal cancer surveillance: navigating unexplained elevations and the challenge of discharge

Despiteendorsement by the National Institute for Health and Care Excellence (NICE), European Society for Medical Oncology (ESMO), National Comprehensive Cancer Network (NCCN) and the Association of Coloproctology of Great Britain and Ireland (ACPGBI), the role of carcinoembryonic antigen (CEA) in post-operative colorectal cancer (CRC) surveillance remains contested with randomised trial evidence demonstrating no overall survival benefit from systematic CEA monitoring. Yet CEA monitoring remains incorporated into surveillance pathways in the UK and internationally, and the clinical scenario of persistently elevated CEA despite comprehensive negative investigation receives little dedicated attention in guidelines or the published literature. This article critically appraises the limitations of CEA in this context, examines the substantial clinical, psychological and resource burden imposed on patients and healthcare systems and explores emerging adjuncts – in particular circulating tumour DNA (ctDNA) – which may enable a more rational, evidence-based approach to investigation and discharge. A structured framework for managing unexplained persistent CEA elevation is proposed.