Tumour markers: uses, benefits and common myths

What are tumour markers?

Many familiar tumour markers are proteins, hormones or other substances measured in blood. Cancer cells may produce them, or other cells may release them in response to a tumour. Some also rise for reasons unrelated to cancer. Examples include prostate-specific antigen (PSA), carcinoembryonic antigen (CEA), cancer antigen 15-3 (CA 15-3) and alpha-fetoprotein (AFP).

Some biomarkers are features of the cancer itself, such as gene changes or proteins found in a tissue sample. They may help select treatment. This article mainly covers substances measured in blood or urine; tests of tumour genes and proteins are explained in our molecular-testing guide. No single marker panel is appropriate for every cancer.

Common markers and their uses

This guide covers commonly used markers and important specialist examples. The same marker can have different roles in different cancers. A test used for monitoring established cancer is not automatically suitable for diagnosing it or screening someone without symptoms.

How markers help guide care

Markers provide a repeatable measurement that can add biological information to examinations and scans. Their contribution ranges from a useful supporting clue to a central part of a cancer-specific treatment pathway. The benefit should be linked to an action the team can take.

Supporting diagnosis and establishing a baseline

Markers can help clarify a suspected tumour type: AFP and beta-hCG in germ-cell tumours, for example, or inhibin in ovarian granulosa-cell tumours. They are interpreted with imaging, pathology and clinical findings under the relevant diagnostic pathway.

A measurement before treatment also provides a baseline. If a marker was raised and reflects the disease, later results can be compared with it. A marker that has never been informative may add little to that person’s monitoring.

Assessing whether treatment is working

A consistent fall in a previously raised marker can support response: CEA in colorectal cancer, CA-125 in ovarian cancer or CA 19-9 in pancreatic cancer, for example. Myeloma response assessment often includes M protein or free light chains. Each disease has its own assessment criteria.

CA 15-3 or CA 27.29 may add information in metastatic breast cancer, especially when disease is difficult to measure directly. They supplement the clinical and imaging assessment; changing therapy solely because the marker changes is not recommended. Early fluctuations also need caution.

Checking for persistent disease and planning follow-up

After treatment, selected markers help look for persistence or recurrence. Examples include CEA in selected colorectal-cancer pathways, PSA after prostate-cancer treatment, thyroglobulin after appropriate treatment for differentiated thyroid cancer, and inhibin in relevant ovarian tumours. The schedule and interpretation differ between these diseases.

Beta-hCG is especially important in gestational trophoblastic disease. Its pattern after treatment can help identify persistent disease, assess response and guide further management. This is a clear example of a marker being central to care. The team follows a dedicated pathway and considers pregnancy and other explanations for an unexpected result.

Estimating prognosis and choosing treatment intensity

Prognosis describes the likely course and outcomes of a disease. In metastatic testicular germ-cell cancer, AFP, beta-hCG and LDH contribute to risk assessment alongside the tumour type, original site and sites of spread.

For metastatic non-seminoma, the degree of marker elevation helps classify disease into good-, intermediate- or poor-prognosis groups. These groups help plan chemotherapy and its duration. Seminoma uses different criteria; a raised AFP is not typical of pure seminoma and requires explanation. Risk groups describe populations, not a fixed outcome for an individual.

Beta-2 microglobulin also contributes to myeloma staging and risk assessment. A prognostic marker estimates risk; it does not necessarily identify which drug will help.

Selecting a treatment in a defined setting

AFP in hepatocellular carcinoma (HCC, a primary liver cancer) provides a specific example. European Medicines Agency (EMA) product information includes ramucirumab as a single-agent option for adults with advanced or unresectable HCC whose serum AFP is at least 400 ng/mL and who have previously received sorafenib. Here, the marker helps define eligibility for a treatment supported by clinical-trial evidence.

The threshold neither diagnoses HCC nor means everyone above it should receive ramucirumab. Liver function, fitness, bleeding risk, previous therapy, alternatives and applicable local prescribing information also matter. Other raised markers do not automatically predict drug benefit.

Identifying when closer reassessment is needed

A persistent, unexplained rise can prompt review, repeat testing or imaging before the next planned visit. The useful outcome is a clearer decision about care. Detecting a biochemical change earlier does not automatically mean starting treatment earlier improves survival or quality of life.

The distinction is particularly important in breast cancer: markers may support monitoring of metastatic disease, but the American Society of Clinical Oncology (ASCO) does not recommend routine CA 15-3, CA 27.29 or CEA testing for surveillance after primary treatment in otherwise asymptomatic patients. Follow-up still matters; it uses the tests supported for that setting.

Understanding the limitations

A useful interpretation considers the cancer, the test method and the circumstances of the sample. A change should lead to an explanation and a plan rather than an automatic label of success or failure.

• Check whether the marker actually tracks this cancer. Some tumours produce little or none of the marker usually associated with them.
• Allow for timing. Markers do not necessarily normalise immediately after surgery or treatment. In germ-cell cancer, the pattern of decline is interpreted in relation to expected clearance and the treatment timeline.
• Use comparable measurements. Different assays, units or laboratories can make trends misleading; anti-thyroglobulin antibodies can interfere with thyroglobulin results.
• Look for non-cancer causes. Bile-duct obstruction can raise CA 19-9; pregnancy raises beta-hCG; vitamin K deficiency or warfarin can affect PIVKA-II; proton-pump inhibitors and impaired kidney function can raise chromogranin A. Do not stop prescribed medicines yourself to improve a result.
• Know the limits of each liver marker. PIVKA-II and AFP-L3 can have selected roles, but are not stand-alone HCC screening tests. For example, the American Association for the Study of Liver Diseases (AASLD) recommends ultrasound with AFP for eligible high-risk surveillance and does not routinely recommend other biomarkers for that purpose.
• Keep the whole assessment in view. A falling marker does not prove cure, and a rising marker does not always mean treatment should change. Symptoms, examination, scans and the relevant clinical pathway remain important.

Common myths

Myth 1 — A high tumour marker means I definitely have cancer

An abnormal result needs an explanation, but cancer is only one possibility. CA-125 can rise with endometriosis or menstruation; PSA with benign prostate enlargement or inflammation; CA 19-9 with a blocked bile duct. These are real biological changes, not necessarily laboratory mistakes.

The next step depends on symptoms, history, examination and other investigations. Treat the highlighted number as a finding to discuss, not a completed diagnosis.

Myth 2 — A normal result means there cannot be cancer

CEA can remain normal in colorectal cancer, and some people produce little CA 19-9 despite a cancer that commonly raises it. A normal result should not override persistent symptoms or an abnormal scan. Ask whether the marker has ever been informative in your disease.

Myth 3 — A tumour-marker package is a complete cancer check-up

For people without symptoms, routinely ordering a panel such as CEA, CA 15-3, CA-125 and CA 19-9 is not an established way to screen for all cancers. Tests useful for monitoring diagnosed disease can be poor screening tests because they may miss early cancer and rise in people without cancer.

When cancer is unlikely before testing, an unexpected abnormality may be more likely to reflect a benign condition than cancer. Adding more unrelated tests creates more opportunities for a misleading result. This can lead to anxiety, repeated blood tests, scans, invasive investigations and expense without a proven improvement in outcomes. A normal package can also give false reassurance.

A specific reason changes the question. PSA screening may be considered after a benefits-and-harms discussion. Eligible people with cirrhosis or selected chronic hepatitis B may need liver-cancer surveillance with imaging and AFP. A suspicious mass or symptoms may justify a selected diagnostic marker. These are defined pathways, not permission to order every available marker.

A family history should prompt an appropriate risk assessment, which may include genetic counselling and cancer-specific screening. It does not automatically justify a broad marker panel. Before testing, ask what the result could change and whether the test is recommended for this particular purpose.

Myth 4 — Any rise means treatment has failed or cancer has returned

A persistent or substantial rise can matter, but the pattern, testing method, symptoms, scans and possible benign causes need review. There is no percentage rise that means failure for every marker and cancer.

The next step may be repeat testing, investigation or a treatment review. Some diseases have specific marker-based decision rules, so a significant rise should not simply be dismissed. Ask when and how the team will act.

Myth 5 — A falling marker proves cure and means treatment can stop

A fall can support response when the cancer produces that marker. It does not prove every cancer cell has gone. Treatment endpoints depend on the cancer and treatment goal. Do not stop medicines or cancel a planned scan because the result enters the reference range.

Myth 6 — The number tells me the stage or how long someone will live

Markers can contribute to staging, prognosis or treatment selection in defined settings. There is no universal conversion from a number to a cancer stage or life expectancy. Comparing your result with another person’s is unreliable; ask how it contributes to your own assessment.

Myth 7 — More frequent testing always gives better protection

Testing helps when the marker and schedule fit a clinical purpose. CEA follow-up in selected colorectal-cancer pathways does not justify the same tests in every cancer. Agree what each result would change and report new symptoms between visits rather than relying on extra blood tests.

Questions to ask your team

Keep a simple record of the test name, date, result, units, laboratory and treatment dates. Bring earlier results to the consultation. A trend is easier to interpret when the team knows where you were in treatment and whether the testing method changed.

• Why is this marker useful in my particular cancer?
• Was it raised before treatment, and has it tracked other findings?
• Could another condition or a different laboratory method explain this change?
• Do we need a repeat test, imaging or another investigation?
• What is the next step, and which symptoms should prompt earlier contact?

Common questions

Related reading

• How doctors assess whether cancer treatment is working
• Molecular and genetic testing
• Liquid biopsy and circulating tumour DNA