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Tumour markers are substances that are made by cancer cells or by normal cells in response to cancer. Most people have these substances at a low level in their blood, but the amount of each marker can increase, sometimes a lot, when there is cancer in the body. Some tumour markers are specific to one type of cancer, while others may be present in many different types of cancer.
There are many different types of tumour markers, including:
- alpha-fetoprotein (AFP)
- cancer antigen 125 (CA125)
- cancer antigen 15-3 (CA15-3)
- carbohydrate antigen 19-9 (CA19-9)
- carcinoembryonic antigen (CEA)
- human chorionic gonadotropin (hCG or beta-hCG)
- prostate-specific antigen (PSA)
Tumour markers are sometimes called biomarkers.
Why tumour marker tests are done
Tumour marker tests are done to:
- look for cancer in people who have a strong family history of a particular cancer but don’t have symptoms (screening)
- diagnose cancer
- see how far the cancer has spread (staging)
- predict how aggressive the cancer is likely to be
- predict what treatment the cancer is likely to respond to
- predict how likely it is that the cancer will come back (recur) after treatment
- find out if cancer treatment is working or see if cancer has come back after treatment
How tumour marker tests are done
Tumour marker tests are usually done in a lab or hospital. You don’t usually need to do anything to prepare for these tests.
A lab technologist will take a sample of your blood. The blood sample is then analyzed using special machines.
If a tumour marker is being used to see if the treatment is working or to see if the cancer has come back, it will be measured in many samples taken over a period of time (called serial measurements).
What the results mean
A tumour marker test on its own is not enough to screen for or diagnose cancer. Tumour marker test results should be combined with:
- a thorough medical history
- a physical exam
- other lab tests
- imaging tests
If a tumour marker test is being used to monitor how treatment is working, your test results may be compared to results from before the start of treatment.
If tumour marker levels decrease or return to normal, it may mean that treatment is working, especially if levels were increased before treatment.
An increase in tumour marker levels may mean the cancer is not responding to treatment, is growing or has come back (recurred). A slight increase may not be significant. The doctor looks at trends in the increase over time.
Chemotherapy treatment can cause a temporary increase in tumour marker levels. This happens because chemotherapy causes cancer cells to die quickly and release large amounts of the tumour marker.
What happens if the results are abnormal
Your doctor may recommend more tests, procedures, follow-up care or treatment.
Limitations of tumour markers
There are limitations to tumour markers. Other tests are usually needed to diagnose cancer or find out if cancer has come back after treatment. Some limitations of tumour markers include:
- A non-cancerous disease or condition can increase tumour marker levels. Some tumour markers can be high in people who do not have cancer.
- Some tumour markers are specific to a particular type of cancer, while others may be elevated in many types of cancer.
- Tumour marker levels may not rise until the cancer worsens. This is not helpful for finding cancer early or finding out if cancer has come back after treatment.
- Some cancers do not have known tumour markers.
- Some people do not have higher tumour marker levels even if the type of cancer they have usually makes tumour markers.
Checking or testing for a disease in a group of people who don’t show any symptoms of the disease.
Examples of cancer screening tests include mammography, colonoscopy and Pap test.
Organized screening programs are offered to groups of people through a coordinated program. Opportunistic (or ad hoc) screening is offered outside of an organized screening program (for example, some women have Pap tests at their doctor’s office during a physical exam).
What’s the lifetime risk of getting cancer?
The latest Canadian Cancer Statistics report shows about half of Canadians are expected to be diagnosed with cancer in their lifetime.