⚕️ Educational content only. This article explains tumour markers from a biomedical science perspective. It is not medical advice, and does not constitute diagnosis or guidance on treatment. Always consult a qualified healthcare professional.
Tumour markers are substances — often proteins — produced by cancer cells or by the body in response to cancer. They are measured in blood, urine, or tissue samples and used alongside imaging and biopsy in clinical oncology. Understanding what each marker measures and its limitations is core to biomedical laboratory science.
Key Takeaways
- Tumour markers are not used as standalone screening tools in most cancers due to low specificity.
- PSA monitors prostate cancer; CA-125 monitors ovarian cancer; CEA monitors colorectal cancer; AFP monitors liver and germ cell tumours.
- Elevated levels can occur in benign conditions, so results are always interpreted with clinical context.
- Serial measurements (tracking change over time) are often more useful than a single result.
What Are Tumour Markers?
Tumour markers are biological molecules found in blood or other body fluids that may be elevated when cancer is present. They include proteins, hormones, enzymes, and genetic material. No tumour marker is 100% specific — many are elevated in benign disease, inflammation, or normal physiological states. This limits their value as standalone screening tools, but makes them highly useful for monitoring known cancer, assessing treatment response, and detecting recurrence.
PSA — Prostate-Specific Antigen
PSA is a serine protease produced by prostatic epithelial cells. It is organ-specific (prostate) but not cancer-specific. Elevated PSA (>4 ng/mL conventionally, though thresholds vary) can indicate prostate cancer, benign prostatic hyperplasia (BPH), prostatitis, or urinary tract infection. PSA is used to monitor men with diagnosed prostate cancer and to detect recurrence after treatment. PSA velocity (rate of rise) and PSA density (PSA relative to prostate volume) improve specificity. Free-to-total PSA ratio may also be assessed — a lower ratio suggests higher cancer probability.
CA-125 — Cancer Antigen 125
CA-125 is a glycoprotein encoded by the MUC16 gene and expressed on the surface of ovarian epithelial cells. It is primarily used to monitor epithelial ovarian cancer. Elevated CA-125 (>35 U/mL) is also seen in endometriosis, fibroids, pelvic inflammatory disease, and during menstruation, meaning it has limited value as a screening test in pre-menopausal women. Post-menopausal women with a pelvic mass and elevated CA-125 have a high positive predictive value for malignancy.
CEA — Carcinoembryonic Antigen
CEA is a glycoprotein involved in cell adhesion, produced during foetal development and normally present at very low levels in healthy adults. Elevated CEA is associated with colorectal, lung, gastric, pancreatic, and breast cancers. It is used primarily to monitor treatment response and detect recurrence in known colorectal cancer rather than for diagnosis. Non-malignant causes of raised CEA include smoking, cirrhosis, inflammatory bowel disease, and pancreatitis.
AFP — Alpha-Fetoprotein
AFP is produced by the yolk sac and foetal liver. In adults, elevated AFP is associated with hepatocellular carcinoma (HCC) and non-seminomatous germ cell tumours (NSGCTs) of the testis or ovary. AFP is used alongside ultrasound surveillance for HCC in cirrhotic patients and as part of the tumour marker panel (AFP, βhCG, LDH) for testicular cancer staging and monitoring. Elevated AFP also occurs in hepatitis, cirrhosis, and during pregnancy.
Other Clinically Used Markers
Additional tumour markers include CA 19-9 (pancreatic and biliary cancers), βhCG (gestational trophoblastic disease and germ cell tumours), LDH (lymphoma, germ cell tumours — reflects tumour burden), and thyroglobulin (monitoring differentiated thyroid cancer post-thyroidectomy). Each is interpreted within a specific clinical and pathological context.
Interpreting Tumour Marker Results
Laboratory reports include a reference range, but tumour markers are rarely diagnostic in isolation. Key principles for interpretation include: (1) serial measurements are more informative than a single value; (2) the clinical picture, imaging, and histology are required for diagnosis; (3) false positives are common in benign disease; (4) some cancers are marker-negative; (5) units and assay methods vary between laboratories, so results from different labs may not be directly comparable.
References
- National Cancer Institute. Tumor Markers. cancer.gov/about-cancer/diagnosis-staging/diagnosis/tumor-markers-fact-sheet
- NHS. Tumour markers. nhs.uk
- Sturgeon CM, et al. National Academy of Clinical Biochemistry Laboratory Medicine Practice Guidelines for use of tumour markers. Clin Chem. 2008.