Types, Usage and Limits
A tumor marker is a substance found in your blood, urine, or body tissue. The term "tumor markers" may refer to proteins that are made by both healthy cells and cancer cells in the body. It may also refer to mutations, changes, or patterns in a tumor's DNA. Tumor markers are also called biomarkers.
A tumor marker is anything present in or produced by cancer cells or other cells of the body in response to cancer or certain benign (noncancerous) conditions that provides information about a cancer, such as how aggressive it is, what kind of treatment it may respond to, or whether it is responding to treatment.
Tumor markers have traditionally been proteins or other substances that are made at higher amounts by cancer cells than normal cells. These can be found in the blood, urine, stool, tumors, or other tissues or bodily fluids of some patients with cancer. Increasingly, however, genomic markers (such as tumor gene mutations, patterns of tumor gene expression, and nongenetic changes in tumor DNA) that are found in tumors themselves and in tumor fragments shed into bodily fluids are being used.
Many different tumor markers have been characterized and are in clinical use. Some are associated with only one type of cancer, whereas others are associated with multiple different cancer types
Doctors may use tumor marker tests to learn if you have cancer. These tests can also help doctors to learn more about your cancer and help to plan treatment.
There are two main types of tumor markers: circulating tumor markers and tumor tissue markers.
Circulating tumor markers
can be found in the blood, urine, stool, or other bodily fluids of some patients with cancer. Circulating tumor markers are used to:
- estimate prognosis
- determine the stage of cancer
- detect cancer that remains after treatment (residual disease) or that has returned after treatment
- assess how well a treatment is working
- monitor whether the treatment has stopped working
Although an elevated level of a circulating tumor marker may suggest the presence of cancer and can sometimes help to diagnose cancer, this alone is not enough to diagnose cancer. For example, noncancerous conditions can sometimes cause the levels of certain tumor markers to increase. In addition, not everyone with a particular type of cancer will have a higher level of a tumor marker associated with that cancer. Therefore, measurements of circulating tumor markers are usually combined with the results of other tests, such as biopsies or imaging, to diagnose cancer.
Tumor markers may also be measured periodically during cancer therapy. Such “serial measurements,” which show how the level of a marker is changing over time, are usually more meaningful than a single measurement. For example, a decrease in the level of a circulating tumor marker may indicate that the cancer is responding to treatment, whereas an increasing or unchanged level may indicate that the cancer is not responding.
Circulating tumor markers may also be measured periodically after treatment has ended to check for recurrence (the return of cancer).
Tumor tissue (or cell) markers
are found in the actual tumors themselves, typically in a sample of the tumor that is removed during a biopsy. Tumor tissue markers are used to:
- diagnose, stage, and/or classify cancer
- estimate prognosis
- select an appropriate treatment (e.g., treatment with a targeted therapy)
Tumor tissue markers that indicate whether someone is a candidate for a particular targeted therapy are sometimes referred to as biomarkers for cancer treatment. Tests for these biomarkers are usually genetic tests that look for changes in genes that affect cancer growth.
Examples of tumor tissue markers that are used as biomarkers for cancer treatment include estrogen receptor and progesterone receptor, which are tested for to determine whether someone with breast cancer should get treatment with hormone therapy.
Because some tumors shed cells and genetic material into blood, it is sometimes possible to examine biomarkers in blood samples. Although these "liquid biopsies" are not yet routinely used, they have several potential advantages. Because they don’t involve surgery, they can be done more frequently than standard biopsies. They can also be performed when surgical biopsies cannot, such as when tumors are difficult to reach or patients can’t tolerate surgery.
High tumor marker levels can be a sign of cancer. Along with other tests, tumor marker tests can help doctors diagnose specific types of cancer and plan treatment. Tumor marker tests are most commonly used to do the following:
- Learn if a person has cancer. Higher tumor marker levels may indicate a certain type of cancer. A tumor marker test may be used as a part of your initial diagnosis.
- Guide treatment decisions. Some tumor marker tests tell doctors if they should give chemotherapy or immunotherapy. Others help doctors choose which drugs may work best.
- Check the progress of treatment. Changes in your tumor marker levels can show how well the treatment is working.
- Predict the chance of recovery. Tumor markers can help doctors predict the cancer's behavior and response to treatment. They can also predict your chance of recovery.
- Predict or watch for recurrence. Recurrence is when cancer comes back after treatment. Tumor marker tests can help predict how likely this is. That's why these tests might be part of your care after treatment ends. They may help find a recurrence sooner than other tests.
- Tumor marker tests may also be used to look for cancer in people with a high risk of the disease. Or you might have these tests to learn more about the cancer when doctors first find it.
Tumor marker tests are not perfect. They are often not specific for cancer and may not be sensitive enough to pick up a cancer recurrence. The presence of tumor markers alone is not enough to diagnose cancer. You will probably need other tests to learn more about a possible cancer or recurrence. Some limits to tumor marker tests are listed below.
- A condition or disease that is not cancer can raise tumor marker levels.
- People without cancer can have high tumor marker levels.
- Tumor marker levels can change over time. The tests may not get the same result every time.
- Tumor marker levels may not go up until cancer gets worse. This does not help find cancer early, or in people at high risk. It also does not help find a recurrence.
- Some cancers do not make tumor markers that are found in the blood. And, some types of cancer have no known tumor markers.
- Your tumor marker levels might not go up, even if your type of cancer usually makes tumor markers.
How is a tumor marker test done?
A member of your health care team will take a sample of your blood or urine. The sample goes to a laboratory for testing. Some tumor marker tests must be done more than once, because the levels of tumor markers can change regularly.
You will also need other tests to find cancer and check on treatment. This is because tumor marker results have limitations (see above) and are sometimes wrong. They might:
Show a tumor is present or growing when it is not.
Show there is no tumor when one is present, or show treatment is working when it is not.
No test is perfect. So, your doctor will probably order several types of tests to find answers.
Doctors use different tumor marker tests for different cancers. However, many cancers do not yet have tumor markers that can help guide care.
Questions to ask the health care team about Tumor Makers
You might want to ask your health care team these questions:
- Do you think I need any tumor marker tests? Which ones, and why?
- Have you looked for tumor markers already? Which ones?
- How are these tests done? How often should I have them?
- Who can explain the results to me?
- If I have abnormal levels of a tumor marker, what does that mean? How could this result affect my treatment plan?
- Will I need tumor marker tests after my cancer treatment ends?
- Where can I learn more about tumor markers and testing?
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