Understanding tumour markers
BMJ 2008; 336 doi: https://doi.org/10.1136/sbmj.0801035 (Published 01 January 2008) Cite this as: BMJ 2008;336:0801035
- Kunal Kulkarni, foundation year trainee1,
- Sasha Abraham, foundation year trainee2,
- Iain McNeish, senior lecturer/honorary consultant in medical oncology3
- 1Oxford Deanery
- 2London Deanery
- 3St Bartholomew's Hospital, London
A total of 153 397 people died from cancer in the UK in 2004. Worldwide, the number dying from cancer exceeded 6 million—12% of deaths. The World Health Organization (WHO) predicts that cancer rates could rise by 50% to 15 million newly diagnosed cases by the year 2020, which means that cancer will play an increasingly important role in all our careers.1
Despite the absence of established screening programmes, terms such as PSA are increasingly becoming publicly synonymous with cancer screening. Tumour markers are often branded among patients and doctors as “cancer blood tests”—direct signposts to cancer. Is this claim justified or is their role in cancer management a little different?
What are tumour markers?
Tumour markers are proteins. As cancer is essentially the unregulated growth of normal tissue, both malignant and non-malignant tissues produce these proteins. This dramatically reduces their specificity and sensitivity as diagnostic tools.
A number of the commonly encountered markers are classed as tumour antigens. These include markers such as carcinoembryonic antigen (CEA), α fetoprotein (AFP), and the cancer antigens CA 125 and CA19-9, which are detected by both monoclonal and polyclonal antibodies (antibodies directed against the antigen). Some of these (such as AFP) are known as oncofetal antigens, as they are present in normal fetuses and diminish to undetectable levels in adults, often reappearing with certain cancers.
Markers are usually either “cancer specific” (directly associated with the presence of neoplastic tissue, such as CEA, CA19-9, CA 125) or “tissue specific” (not specifically linked to the tumour, but associated with the specific tissues that are undergoing neoplastic change, such as AFP, β human chorionic gonadotrophin (β-hCG), PSA). Although the tissue specific factors may help localise the affected …
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