Introduction
A blood test showing an elevated tumour marker can understandably cause concern. But does a high tumour marker level automatically mean cancer? Not necessarily.
Tumour markers are substances that may be produced by cancer cells or by normal cells in response to certain conditions. Some can be measured through blood tests and may help doctors assess specific cancers, monitor treatment response or identify signs of recurrence.
Four commonly discussed tumour markers are CEA, CA-125, CA 19-9 and AFP. Each is associated with particular cancers, but none can independently confirm or rule out cancer.
Understanding what these tests measure, when doctors recommend them and what their results actually mean can help avoid unnecessary fear and misinterpretation.
What Are Tumour Markers?
Tumour markers are biological substances found in blood, urine, body fluids or tissue. They may be produced by tumour cells or by the body in response to a tumour.
Some tumour markers are proteins, while others are hormones, enzymes or genetic substances.
Doctors may recommend tumour marker tests for different reasons:
- Supporting diagnosis: They may provide additional information when cancer is suspected.
- Monitoring treatment: Changes in marker levels may help assess how a cancer responds to treatment.
- Detecting recurrence: A rising level after treatment may indicate the need for further evaluation.
- Assessing disease activity: In selected cancers, marker levels may help doctors understand disease progression.
However, tumour markers are not universally suitable for cancer screening. Some may increase due to non-cancerous conditions, while certain cancers may not produce elevated marker levels at all.
1. CEA Test – Carcinoembryonic Antigen
What is CEA?
Carcinoembryonic antigen (CEA) is a protein that can be present at higher levels in certain cancers, particularly colorectal cancer.
The CEA test measures the amount of this protein in the blood. It is mainly used to monitor people who have already been diagnosed with certain cancers, rather than to screen healthy individuals.
Cancers associated with elevated CEA
CEA may be elevated in:
- Colorectal cancer
- Pancreatic cancer
- Stomach cancer
- Lung cancer
- Breast cancer
- Certain other cancers
Non-cancerous reasons for high CEA
An elevated CEA level does not always indicate cancer. It may also occur with:
- Smoking
- Liver disease
- Inflammatory bowel conditions
- Pancreatitis
- Certain infections and inflammatory conditions
When is a CEA test recommended?
Doctors may use CEA testing to:
- Establish a baseline before treatment in selected patients.
- Monitor response to treatment, particularly in colorectal cancer.
- Follow patients after treatment for signs that may suggest recurrence.
- Support further evaluation when considered alongside symptoms, imaging and other clinical findings.
Important: CEA is not recommended as a standalone screening test for colorectal cancer in people without a diagnosis.
2. CA-125 Test – Cancer Antigen 125
What is CA-125?
CA-125 is a protein found on the surface of certain cells, including cells associated with the ovaries and the lining of the abdomen and chest.
The CA-125 blood test is commonly associated with ovarian cancer evaluation and monitoring. However, elevated CA-125 levels can also occur in several non-cancerous conditions.
Cancers associated with elevated CA-125
CA-125 may be elevated in:
- Ovarian cancer, particularly some epithelial ovarian cancers
- Fallopian tube cancer
- Primary peritoneal cancer
- Certain other cancers, including endometrial and pancreatic cancers
Non-cancerous reasons for high CA-125
CA-125 may increase due to:
- Menstruation
- Pregnancy
- Endometriosis
- Uterine fibroids
- Pelvic inflammatory disease
- Liver disease
- Other conditions causing inflammation or fluid accumulation in the abdomen or chest
When is a CA-125 test recommended?
A doctor may recommend CA-125 testing:
- As part of the evaluation of a suspicious ovarian or pelvic mass.
- To monitor certain patients receiving treatment for ovarian cancer.
- During follow-up after treatment, when clinically appropriate.
- Alongside imaging and other investigations when symptoms or examination findings require further assessment.
Important: CA-125 alone cannot diagnose ovarian cancer. It is also not recommended as a routine screening test for ovarian cancer in average-risk women without symptoms because screening has not been shown to reduce ovarian cancer deaths and can lead to false-positive results and unnecessary procedures.
3. CA 19-9 Test – Cancer Antigen 19-9
What is CA 19-9?
CA 19-9 is a carbohydrate antigen that may be released into the bloodstream by certain cancer cells. It is most commonly associated with pancreatic cancer and may also be elevated in some gastrointestinal cancers.
The CA 19-9 test is primarily used to help monitor selected patients with pancreatic cancer and assess treatment response alongside other clinical findings.
Cancers associated with elevated CA 19-9
Elevated CA 19-9 levels may be seen in:
- Pancreatic cancer
- Bile duct cancer (cholangiocarcinoma)
- Gallbladder cancer
- Stomach cancer
- Colorectal cancer
Non-cancerous reasons for high CA 19-9
CA 19-9 can also increase in conditions such as:
- Gallstones
- Bile duct obstruction
- Pancreatitis
- Liver disease
- Biliary tract inflammation
In particular, bile duct obstruction can cause a significant rise in CA 19-9, even without cancer.
When is a CA 19-9 test recommended?
Doctors may recommend this test to:
- Monitor certain patients diagnosed with pancreatic cancer.
- Assess changes during treatment.
- Support follow-up after treatment.
- Provide additional information when pancreatic or biliary cancer is suspected.
Important: CA 19-9 is not suitable for general pancreatic cancer screening. Some people do not produce CA 19-9 even when they have pancreatic cancer, so a normal result cannot rule out the disease.
4. AFP Test – Alpha-Fetoprotein
What is AFP?
Alpha-fetoprotein (AFP) is a protein produced mainly by the developing liver and yolk sac during pregnancy. AFP levels are normally high in the developing fetus and decrease after birth.
In adults, elevated AFP may be associated with certain cancers, particularly hepatocellular carcinoma (a type of liver cancer) and some germ cell tumours.
Cancers associated with elevated AFP
AFP may be elevated in:
- Hepatocellular carcinoma (primary liver cancer)
- Certain non-seminomatous germ cell tumours of the testis
- Certain ovarian germ cell tumours
- Some other germ cell tumours
Non-cancerous reasons for high AFP
AFP may also increase due to:
- Chronic hepatitis
- Liver cirrhosis
- Liver regeneration or inflammation
- Pregnancy
When is an AFP test recommended?
Doctors may recommend AFP testing:
- Alongside liver imaging in selected people at increased risk of hepatocellular carcinoma.
- As part of the evaluation of certain suspected germ cell tumours.
- To monitor treatment response in AFP-producing cancers.
- During follow-up when recurrence is a concern.
Important: AFP is not a standalone diagnostic test for liver cancer. Some liver cancers do not produce elevated AFP, while non-cancerous liver conditions can also increase its levels.
CEA vs CA-125 vs CA 19-9 vs AFP: Key Differences
| Tumour marker | Common cancer association | Main clinical use |
| CEA | Colorectal cancer | Monitoring selected colorectal cancer patients |
| CA-125 | Ovarian cancer | Evaluation and monitoring in selected patients |
| CA 19-9 | Pancreatic cancer | Monitoring selected pancreatic cancer patients |
| AFP | Liver cancer and certain germ cell tumours | Evaluation and monitoring in selected patients |
These associations are not exclusive. A tumour marker may be elevated in more than one cancer, and the same cancer may not cause an elevation in every patient.
Can a High Tumour Marker Level Confirm Cancer?
No. An elevated tumour marker level does not automatically mean that a person has cancer.
Tumour markers have limitations:
1. False-positive results: Non-cancerous conditions, inflammation, infections and other medical conditions may increase marker levels.
2. False-negative results: Some people with cancer may have normal tumour marker levels because their tumour does not produce the marker or produces it in very small amounts.
3. Limited specificity: A marker may be associated with multiple cancers and non-cancerous conditions. It cannot always identify where a problem is located.
4. Individual variation: Marker levels can vary between individuals and may be influenced by the type, stage and biological characteristics of a tumour.
5. Results need clinical context: A single result is rarely enough to make a diagnosis. Doctors may consider symptoms, medical history, physical examination, imaging, biopsy and changes in marker levels over time.
What Happens If Your Tumour Marker Is Elevated?
If a tumour marker result is higher than the laboratory's reference range, it is important not to panic or assume that cancer is present.
Your doctor may recommend the following steps depending on your medical history and the marker involved:
- Review the result: Check the measured value, laboratory reference range and previous reports, if available.
- Assess symptoms and medical history: Consider relevant symptoms, existing conditions, medications and risk factors.
- Investigate possible non-cancerous causes: Conditions such as inflammation, liver disease or bile duct obstruction may affect certain markers.
- Consider imaging: Ultrasound, CT, MRI or other imaging may be advised depending on the suspected condition.
- Repeat testing if appropriate: Tracking the marker over time may provide more useful information than a single measurement.
- Consider further diagnostic procedures: A biopsy or other investigation may be required when clinically indicated.
The next step should always be guided by a qualified healthcare professional.
Are Tumour Marker Tests Used for Routine Cancer Screening?
Most tumour marker tests are not recommended for routine cancer screening in healthy people at average risk.
For example:
- CEA is not a substitute for recommended colorectal cancer screening.
- CA-125 is not recommended for routine ovarian cancer screening in average-risk women without symptoms.
- CA 19-9 is not recommended for general pancreatic cancer screening.
- AFP may be used in surveillance for selected people at high risk of liver cancer, usually alongside imaging, rather than as a universal screening test.
Cancer screening recommendations depend on age, sex, family history, personal medical history and individual risk factors. A doctor can help determine which screening tests are appropriate.
Conclusion
Tumour markers such as CEA, CA-125, CA 19-9 and AFP can provide useful clinical information, particularly when monitoring certain cancers or supporting further investigation. However, they are not definitive cancer tests and should never be interpreted in isolation.
A high result does not automatically mean cancer, and a normal result does not guarantee that cancer is absent. Understanding the purpose and limitations of each test helps people make informed decisions and avoid unnecessary anxiety.
Medical Disclaimer: This article is intended for general educational and awareness purposes only. It is not a substitute for medical diagnosis, treatment or professional medical advice. Health screening recommendations vary according to age, sex, symptoms, medical history, medications, family history and individual risk factors. Please consult a qualified healthcare professional before deciding which tests or screenings are appropriate. Do not start, stop or change medication based solely on information in this article.
