Understanding Tumor Markers in Your Blood Test

Section Editor: Christopher McCudden Ph.D., DABCC, FADLM, FCACB
July 7, 2026

Tumor markers are substances, usually proteins, that can be measured in a blood sample. They may be produced by cancer cells or by normal cells reacting to a cancer. When a tumor marker is measured, the result is reported as a number, which is then compared to a range of values typically seen in people without cancer. A single tumor marker blood test is rarely used on its own to diagnose or rule out cancer. Instead, tumor markers are most useful when followed over time and interpreted alongside imaging, a physical examination, and, when needed, a biopsy.

This article explains what tumor markers are, how they are used, and, just as importantly, their limits. It then describes the individual tumor markers you are most likely to see on a blood test report, so you can match the name on your report to its meaning.

The reference range that applies to your result is the one printed on your laboratory report, not the typical ranges shown here. Reference ranges vary between laboratories based on the equipment used, the population tested, and individual factors such as age, sex, and pregnancy status. Always compare your result to the reference range printed on your own report, and discuss any abnormal result with your doctor.

What are tumor markers?

Tumor markers are substances that can be measured in the blood and may rise when cancer is present. Most are proteins. Some are made by the cancer cells themselves, and others are made by healthy cells in response to a cancer. Because the same substances are often present in small amounts in people without cancer, and can rise in non-cancerous conditions, tumor markers are not simple yes-or-no cancer tests.

Tumor markers measured in the blood are not the same as the tumor biomarkers measured in a tissue sample after a biopsy or surgery. Tissue biomarkers, such as hormone receptors or specific gene changes, are features of the cancer itself and are used to choose targeted treatments. Those tests are described in our Biomarkers and Molecular Testing section. The blood tumor markers described here are primarily used to monitor a known cancer over time.

How are tumor markers tested?

Tumor markers are measured from a blood sample drawn from a vein, usually without any special preparation. Each marker is measured by its own laboratory test, and the result is given as a number with units. Because different laboratories and different testing methods can produce slightly different values, the trend in a tumor marker measured at the same laboratory over time is usually more meaningful than any single result. For this reason, tumor markers are often measured repeatedly, for example before treatment, during treatment, and at follow-up visits.

How are tumor markers used?

Tumor markers are used in a few specific ways, and understanding which one applies to you helps make sense of the result. Their main uses are:

Monitoring response to treatment — In a person already diagnosed with cancer, a marker that falls during treatment suggests the treatment is working, while a marker that stays high or rises may prompt a change in approach.
Watching for recurrence — After treatment, a marker that begins to rise over several measurements can be an early sign that a cancer has come back, often before symptoms appear.
Helping with diagnosis — A tumor marker can support a diagnosis when it is combined with imaging and a biopsy, but it is almost never used to make a diagnosis on its own.
Screening in specific situations — A few markers are used to look for cancer in people without symptoms, but only in particular circumstances, such as PSA testing after a discussion of its benefits and harms, or alpha-fetoprotein testing along with ultrasound in people with cirrhosis. Most tumor markers are not useful for general screening.

Across all of these uses, the pattern over time usually matters more than a single value, and a tumor marker result is one piece of information that guides decisions rather than a diagnosis by itself. These traditional tumor markers are also different from newer multi-cancer early detection blood tests, which look for signs of several cancers at once and are still being studied.

Important limitations of tumor markers

Tumor markers have real limits, and knowing them prevents unnecessary worry or false reassurance. They are not specific to cancer, which means non-cancerous conditions can raise them. They are also not perfectly sensitive, which means a normal level does not rule out cancer, and some cancers never raise a marker at all. A single mildly elevated result is often not significant on its own and is typically repeated before any further action is taken. Because of these limitations, a tumor marker is always interpreted alongside the clinical picture, imaging, and, when needed, a biopsy, rather than in isolation.

Common tumor markers and what they mean

The tumor markers below are the ones most often seen on a blood test report. For each, it helps to know which cancers it is linked to, how it is generally used, and what else can raise it.

PSA (prostate-specific antigen)

PSA is a protein made by the prostate gland. It is used to help screen for and monitor prostate cancer. Whether to use PSA for screening is a personal decision made with a doctor after weighing the possible benefits and harms, rather than an automatic test for everyone. PSA can also be raised by non-cancerous conditions, including an enlarged prostate (benign prostatic hyperplasia), inflammation of the prostate (prostatitis), a recent urinary infection, recent ejaculation, or vigorous cycling. After treatment for prostate cancer, PSA is one of the main tools used to watch for the cancer returning.

CEA (carcinoembryonic antigen)

CEA is used mainly to monitor colorectal cancer during and after treatment, and it is sometimes elevated in other cancers of the digestive tract, lung, and breast. It is not used to screen for cancer in people without symptoms. CEA can be raised by non-cancerous conditions as well, and smoking is a common cause of a mildly elevated level.

AFP (alpha-fetoprotein)

AFP is used in the diagnosis and monitoring of liver cancer (hepatocellular carcinoma) and certain germ cell tumors of the testis or ovary. Along with ultrasound, it is also used to watch for liver cancer in people with cirrhosis. AFP is normally high during pregnancy and can be raised by non-cancerous liver conditions such as hepatitis, so an elevated level does not always mean cancer.

CA 19-9

CA 19-9 is most commonly used to monitor cancers of the pancreas and bile ducts. It can also be raised by non-cancerous conditions that block the bile ducts, and by inflammation of the pancreas (pancreatitis). Some people do not produce CA 19-9 at all, which means a normal level does not rule out cancer in them. Because of these limits, CA 19-9 is not used to screen for cancer.

CA 125

CA 125 is used mainly to monitor ovarian cancer during and after treatment. It is often raised by common non-cancerous conditions, including menstruation, endometriosis, uterine fibroids, pregnancy, and benign ovarian cysts, which is why it is not reliable for screening the general population. When a pelvic mass is being assessed, CA 125 is sometimes combined with another marker called HE4 to help judge how likely the mass is to be cancer.

CA 15-3 and CA 27-29

CA 15-3 and CA 27-29 are two related markers used mainly to monitor advanced or metastatic breast cancer during and after treatment. They are not used to screen for or diagnose early breast cancer, because they are often normal when a breast cancer is small and early.

Beta-hCG (human chorionic gonadotropin)

Beta-hCG is used mainly for germ cell tumors of the testis or ovary and for gestational trophoblastic disease, a group of tumors that arise from placental tissue. It is also the hormone measured by pregnancy tests, so it is normally high during pregnancy. In germ cell tumors, beta-hCG is often measured together with AFP.

Calcitonin

Calcitonin is a hormone made by certain cells in the thyroid gland. It is used to help diagnose and monitor a specific type of thyroid cancer called medullary thyroid carcinoma. Because this cancer can run in families, calcitonin may also be checked in people with a known family history or an inherited risk.

Thyroglobulin

Thyroglobulin is a protein made by normal thyroid tissue and by most differentiated thyroid cancers (the papillary and follicular types). After the thyroid gland has been removed to treat thyroid cancer, thyroglobulin is used to watch for the cancer coming back. Antibodies to thyroglobulin can interfere with the test, so they are usually measured at the same time.

What can cause a high tumor marker result besides cancer?

A raised tumor marker often has a cause other than cancer, which is why the result is interpreted carefully rather than taken as proof of cancer. Common non-cancerous causes include inflammation and infection, benign conditions of the organ that makes the marker (such as an enlarged prostate for PSA, endometriosis for CA 125, or liver disease for AFP), and blockage of the bile ducts for CA 19-9. Smoking can raise CEA. Pregnancy raises beta-hCG and AFP, and menstruation can raise CA 125. Reduced kidney or liver function can affect the level of some markers. Finally, differences between laboratories and testing methods, and occasionally interfering antibodies in the blood, can produce a falsely high result. For all of these reasons, a single elevated tumor marker is frequently repeated and placed in context before any further step is taken.

What happens after an abnormal tumor marker result?

An abnormal tumor marker result guides the next steps rather than providing a diagnosis on its own. Because a single value can be misleading, the test is often repeated to determine whether the level is stable, rising, or falling, since the trend is usually more informative than a single measurement. Depending on the situation, the result may lead to imaging, such as ultrasound, CT, or MRI, and, if a suspicious area is found, to a biopsy to confirm whether cancer is present. In a person already being treated or followed for cancer, a rising marker may prompt earlier imaging to check for a return of the disease. Your doctor will interpret the result together with your history, examination, and other tests, and will explain what, if anything, needs to happen next.

Questions to ask your doctor

Which tumor marker was measured, and why was it ordered for me?
Is this test being used to help diagnose a problem, to monitor a known cancer, or to watch for recurrence?
What is my result, and how does it compare to previous measurements?
Could a non-cancerous condition explain my result?
Will this test be repeated, and if so, when?
Does my result mean I need imaging or a biopsy?
Should my results always be measured at the same laboratory to track the trend?
What level of change in this marker would be considered meaningful?
If I am being monitored after treatment, how will this marker be used to guide follow-up?
Who should I contact if I have questions about a future result?