Tumor Markers: A Guide to Cancer-Related Blood Tests
Tumor markers are substances that can be measured in blood, urine, or tissue. They are sometimes produced by cancer cells or by the body in response to cancer. This guide explains what tumor marker tests are for, how doctors interpret them, and why they are rarely used on their own to diagnose cancer.
Key takeaways
- Tumor markers are substances found in blood, urine, or tissue that may be elevated in some cancers.
- Most tumor markers are not specific enough to diagnose cancer by themselves.
- Tumor markers are often used to monitor response to treatment or detect recurrence after treatment.
- A normal tumor marker level does not rule out cancer, and an elevated level does not always mean cancer is present.
- Tumor marker testing should be interpreted by a healthcare provider alongside imaging, biopsy, and clinical findings.
What Are Tumor Markers?
Tumor markers are biological substances that can be detected in body fluids or tissues. Some are produced directly by cancer cells, while others are made by normal cells in response to cancer or other conditions. Common examples include prostate-specific antigen (PSA), carcinoembryonic antigen (CEA), alpha-fetoprotein (AFP), CA-125, and CA 19-9. These markers can be measured with laboratory tests, most often using a blood sample.
It is important to understand that tumor markers are not cancer-specific in most cases. Many non-cancerous conditions, such as inflammation, infection, or benign tumors, can also raise marker levels. Likewise, not all cancers produce a detectable marker. This means tumor markers are generally used as one piece of information among many, not as a standalone test for cancer.
How Tumor Markers Are Used in Cancer Care
Tumor markers are most useful when they are measured over time in a specific patient. A single elevated result may be difficult to interpret, but a pattern of rising or falling levels can provide meaningful information. Doctors may use tumor markers to monitor how well a treatment is working, to check for recurrence after treatment, or to help distinguish between different types of cancer when combined with other tests.
In some cases, tumor markers are used alongside imaging and biopsy to help guide decisions. For example, PSA is commonly used to screen for prostate cancer in certain men after a discussion with their doctor. AFP may be used in people with liver disease who are at higher risk of liver cancer. However, routine screening with tumor markers for the general population is not recommended for most cancers because of concerns about false positives and false negatives.
Limitations and Interpretation of Results
Tumor marker tests have important limitations. A false positive occurs when a marker is elevated but no cancer is present, which can lead to unnecessary anxiety and additional testing. A false negative occurs when a marker is normal even though cancer is present. Because of these limitations, tumor markers are not used alone to diagnose cancer. Instead, they are interpreted in the context of a person's medical history, physical exam, imaging studies, and biopsy results.
Reference ranges for tumor markers can vary between laboratories, so results should always be compared to the range provided by the testing lab. A healthcare provider can explain what a specific result means for an individual patient. Changes in marker levels over time are often more informative than a single measurement. Patients should discuss any questions or concerns about tumor marker results with their doctor.
Common Tumor Markers and Their Uses
Several tumor markers are widely used in clinical practice. PSA is used to screen for and monitor prostate cancer. CA-125 is used to monitor ovarian cancer and may be elevated in other conditions such as endometriosis or pelvic inflammatory disease. CEA is often used in colorectal cancer monitoring. AFP is used in liver cancer and germ cell tumors. CA 19-9 is used in pancreatic cancer monitoring, and CA 15-3 and CA 27.29 are used in breast cancer monitoring.
Each marker has its own pattern of usefulness. Some are better for monitoring known disease, while others have a role in screening specific high-risk groups. For example, AFP is sometimes used with ultrasound to screen for liver cancer in people with cirrhosis. It is important to note that no tumor marker is perfect, and testing decisions should be made with a healthcare provider who understands the individual's risk factors and medical history.
Frequently Asked Questions
Can tumor markers diagnose cancer?
No. Tumor markers alone cannot diagnose cancer. They may be elevated in non-cancerous conditions and can be normal in some people with cancer. A cancer diagnosis generally requires a biopsy or other tissue examination.
What causes elevated tumor markers?
Elevated tumor markers can be caused by cancer, but also by benign conditions such as inflammation, infection, liver disease, or kidney disease. Some markers can be elevated due to smoking or other lifestyle factors. A healthcare provider can help interpret the result.
Are tumor markers used for screening?
For most cancers, tumor markers are not recommended for routine screening in the general population. Some markers, such as PSA and AFP, may be used in certain high-risk individuals after a discussion with their doctor.
How often should tumor markers be tested?
The frequency of tumor marker testing depends on the specific cancer, treatment plan, and individual circumstances. Testing is typically ordered by a healthcare provider based on guidelines and the patient's situation.
Sources
Ready to get tested? Compare markers, check any fasting guidance, then secure the panel via the LabTestLocations partner at your convenience.
Order Cancer & Tumor Marker TestsReviewed by the LabTestLocations Editorial Team
The LabTestLocations editorial team reviews laboratory panels against published reference material before publication.