Tumor Markers
A plain-language explanation of what tumor markers are, how they are used in cancer care, and why a single result is read alongside other tests—based on National Cancer Institute resources.
Source: National Cancer Institute · NCI reviewed 2023-12-07 · Verified 2026-07-02
The 30-second version
A tumor marker is anything in or made by cancer cells—or by other cells reacting to cancer or to certain noncancerous conditions—that gives information about a cancer. Markers can help with diagnosis, treatment choices, and follow-up. But an elevated level does not mean someone has cancer, and results are usually combined with other tests like biopsies or imaging.
Key takeaways
- A tumor marker is anything present in or produced by cancer cells, or by other cells responding to cancer or certain benign conditions, that gives information about a cancer.
- An elevated tumor marker level does not mean someone has cancer—noncancerous conditions can also raise a marker.
- Not everyone with a particular cancer will have a higher level of the marker linked to that cancer.
- Because of this, marker measurements are usually combined with other tests, such as biopsies or imaging.
- Markers can help estimate prognosis, guide treatment, show how well treatment is working, and check whether cancer has returned.
- Most tumor markers do not work well for screening people who have no symptoms.
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The simple version
A tumor marker is anything present in or produced by cancer cells—or by other cells of the body in response to cancer or certain benign (noncancerous) conditions—that provides information about a cancer. It can give clues about how aggressive a cancer is, what kind of treatment it may respond to, or whether it is responding to treatment.
A tumor marker is one piece of information, not a diagnosis by itself.
What tumor markers are
Tumor markers have traditionally been proteins or other substances that are made in higher amounts by cancer cells than by normal cells. These can be found in the blood, urine, stool, tumors, or other tissues or bodily fluids of some people with cancer.
Increasingly, genomic markers are also used. These include tumor gene mutations, patterns of tumor gene expression, and nongenetic changes in tumor DNA. Genomic markers are found both in tumors themselves and in tumor fragments shed into bodily fluids.
Many different tumor markers have been described and are in clinical use. Some are associated with only one type of cancer, while others are associated with several cancer types.
Why a single result is not the whole picture
Tumor markers can help diagnose cancer. But having an elevated level of a tumor marker does not mean that someone has cancer. There are two important reasons for this:
- Noncancerous conditions can raise a marker. A benign condition can sometimes cause a marker level to increase.
- Not everyone with a cancer has a raised marker. Not everyone with a particular type of cancer will have a higher level of the marker linked to that cancer.
Because of this, measurements of tumor markers are usually combined with the results of other tests, such as biopsies or imaging, to diagnose cancer.
How tumor markers are used in cancer care
Tumor markers can provide a wide range of information that matters for cancer care:
- Helping to diagnose cancer, alongside other tests.
- The type of cancer.
- The stage of the cancer—how far it has spread.
- An estimate of prognosis, meaning the likely course of the disease.
- What treatment may be effective. Markers that show whether someone is a candidate for a particular targeted therapy are sometimes called biomarkers for cancer treatment. These are generally measured in samples of tumor tissue. Because tumors can shed cells or bits of material into the blood, some markers can also be measured with tests called liquid biopsies.
- How well treatment is working. Measuring a marker again and again ("serial" measurements) during treatment can show whether the tumor is responding.
- Whether cancer has returned. Measuring tumor markers from time to time after treatment ends may be used to check for recurrence.
Where the tests are done
A number of tumor marker tests are used for a wide range of cancer types. Many are carried out by commercial and academic laboratories. Sometimes a cancer center uses a test developed within a single clinical laboratory, known as a lab-developed test, to meet a specific medical need. All tumor markers are tested in laboratories that meet standards set by the Clinical Laboratory Improvement Amendments program.
Tumor markers and screening
Because tumors produce markers that can be measured in blood and other body fluids, researchers hoped these markers might help screen people for cancer—finding it early, before symptoms appear.
However, studies have generally found that circulating tumor markers do not work well for screening. They often do not identify everyone who has the disease (they are not sensitive enough), or they suggest cancer in people who do not actually have it (they are not specific enough).
Researchers are now studying multi-cancer detection tests, which analyze multiple biomarkers in the blood of people without symptoms to try to find early cancers. Many such tests are in development and several are being marketed, but much remains to be learned about how best to use them and about their harms and benefits.
Talk with your health care team about what any specific tumor marker result means for you.
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Tumor Markers: the quick overview
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Suggested animation storyboard▾
- 1Open on a calm title card: "Tumor Markers" with the Cancer Explained mark.
- 2Narrator reads the 30-second summary while a soft animated diagram builds on screen: "A tumor marker is anything in or made by cancer cells—or by other cells reacting to cancer or to certain noncancerous conditions—that gives information about a cancer. Markers can help with diagnosis, treatment choices, and follow-up. But an elevated level does not mean someone has cancer, and results are usually combined with other tests like biopsies or imaging."
- 3Scene 2: illustrate the idea — "A tumor marker is anything present in or produced by cancer cells, or by other cells responding to cancer or certain benign conditions, that gives information about a cancer."
- 4Scene 3: illustrate the idea — "An elevated tumor marker level does not mean someone has cancer—noncancerous conditions can also raise a marker."
- 5Scene 4: illustrate the idea — "Not everyone with a particular cancer will have a higher level of the marker linked to that cancer."
- 6Close on a reminder card: this is educational only; talk with your healthcare team, and a link to the NCI source.
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Quick knowledge check
According to this article, what is a tumor marker?
Frequently asked questions
▸What is a tumor marker?
A tumor marker is anything present in or produced by cancer cells, or by other cells of the body in response to cancer or certain benign (noncancerous) conditions, that provides information about a cancer. It can tell how aggressive the cancer is, what treatment it may respond to, or whether it is responding to treatment.
▸Does a high tumor marker level mean I have cancer?
No. According to the NCI, having an elevated level of a tumor marker does not mean that someone has cancer. Noncancerous conditions can sometimes raise a marker. That is why marker results are usually combined with other tests, such as biopsies or imaging.
▸Where are tumor markers found?
Traditional tumor markers are proteins or other substances that can be found in the blood, urine, stool, tumors, or other tissues or bodily fluids. Increasingly, genomic markers such as tumor gene mutations are also used, and these are found in tumors and in tumor fragments shed into bodily fluids.
▸How do doctors use tumor markers?
Tumor markers can help diagnose cancer, suggest the type and stage of cancer, estimate prognosis, indicate what treatment may work, show how well treatment is working, and check whether cancer has returned after treatment. They are used as one piece of information alongside other tests.
▸Can tumor markers be used to screen for cancer?
Generally, no. Studies have found that circulating tumor markers do not work well for screening people without symptoms. They often miss people who have the disease, or they suggest cancer in people who do not have it. Researchers are still studying newer tests for early detection.
▸What is a liquid biopsy?
Tumors can shed cells or bits of biological material into the blood. Tests that look at tumor markers in blood and other body fluids are sometimes called liquid biopsy tests. They can measure markers used to guide treatment and are being studied for early detection.
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Questions to ask your healthcare team
Consider bringing these questions to your next appointment.
- What is this tumor marker test measuring, and why are you ordering it for me?
- How will you use this result along with my other tests?
- Could a noncancerous condition affect my result?
- What does it mean if my level goes up or down over time?
- Will this test be repeated during or after treatment, and how often?
- Where can I learn more about the specific marker being tested?
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