A tumour marker is a naturally occurring substance in the body that, if present in increased amounts, can indicate the presence of a cancer. Some tumour markers are specific to one type of cancer, while others are related to several different types of cancer. Tumour markers may also increase with non-cancerous conditions.
A tumour marker can be made by cancer cells or by the body in response to cancer. Tumour markers are usually found in the blood or urine, but they can also be found in tumours and other tissue.
There are many different types of tumour markers, including:
Why a tumour marker test is done
Tumour markers can provide information that can be used to help:
- screen for cancer
- Most markers are not used for general screening. Some may be used in people with a strong family history of a particular cancer.
- PSA may be used to screen for prostate cancer.
- diagnose cancer
- stage cancer
- Tumour markers can be used to help determine how far the cancer has spread into other tissues or organs.
- determine a person’s prognosis
- Some markers can help determine how aggressive a cancer is likely to be.
- guide treatment
- Some markers may help doctors predict what treatments the cancer is likely to respond to.
- monitor treatment
- determine recurrence of the cancer
A tumour marker test is done:
- when certain types of cancer are suspected
- to provide a baseline level before treatment
- to check a person’s response to cancer treatment
- to check if cancer has come back (recurred) after treatment
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How a tumour marker test is done
A tumour marker test is usually done in a private laboratory or hospital laboratory. No special preparation is usually needed.
- Most tumour markers are measured using a blood test.
- The blood sample is sent to a laboratory and the tumour marker is analyzed by special machines.
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What the results mean
A tumour marker test alone is not enough to screen for or diagnose cancer. Tumour marker levels may or may not increase when cancer is present. It is also normal for people to have low but detectable levels of tumour markers. Interpretation of tumour marker test results should be combined with:
- thorough medical history
- physical examination
- other laboratory tests
- imaging tests
In monitoring treatment, results of tumour marker tests may be compared to test results before treatment started:
- A decrease in, or return to normal of, the tumour marker level may mean the cancer has responded well to treatment, especially if tumour marker levels were increased before treatment.
- An increase in the tumour marker level may mean the cancer is not responding to treatment, is growing or has come back (has recurred).
- Chemotherapy treatment can cause cancer cells to die quickly and release large amounts of a tumour marker, causing the level to rise. The increase is temporary.
- A slight increase may not be significant. The doctor looks at trends in the increase over time.
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What happens if a change or abnormality is found
The doctor will decide if further tests, procedures, follow-up care or additional treatment are needed.
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