CA 15-3 Test
When you have been or are being treated for breast cancer
A blood sample taken from a vein in your arm
Cancer antigen 15-3 (CA 15-3) is a normal product of breast cells. Concentrations of CA 15-3 in the blood are often increased in breast cancer. CA 15-3 does not cause cancer; rather, it is a protein that is shed by the tumour cells, making it useful as a marker to follow the course of the cancer.
CA 15-3 is rarely elevated in women with localised breast cancer but is increased in about 75% of those with breast cancer that has metastasised (spread to other organs). CA 15-3 also may be elevated in healthy people and in individuals with other cancers, or diseases, such as bowel cancer, lung cancer, cirrhosis, hepatitis, and benign breast disease.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.
How is it used?
CA 15-3 is used as a tumour marker to monitor a patient’s response to breast cancer treatment and to watch for breast cancer recurrence.
CA 15-3 is sometimes also used to give a doctor additional information about where the cancer may have spread (such as into the bones or the liver) and a general sense of how much cancer may be present.
When is it requested?
What does the test result mean?
In general, higher concentrations of CA 15-3 suggest that the breast cancer is more advanced and that a larger amount of tumour is present. The concentration of CA 15-3 tends to increase as the cancer grows. In metastatic breast cancer (cancer that has spread to other organs), the highest concentrations of CA 15-3 are often seen when the cancer has spread to the bones and/or the liver.
Mild to moderate elevations of CA 15-3 also are seen in a variety of other conditions, including liver and pancreatic cancer, cirrhosis, and benign breast disorders as well as in a certain percentage of apparently healthy individuals. The CA 15-3 elevations seen in these non-cancerous conditions tend to be stable over time.
A negative CA 15-3 result (a result below the reference range quoted by the local laboratory) cannot be used to confirm the absence of cancer in a patient. In addition, 25% to 30% of individuals with advanced breast cancer have tumours that do not produce CA 15-3.
Is there anything else I should know?
A test to determine the concentration of CA 15-3 in your blood will not usually be performed immediately after breast cancer treatment begins because there have been instances of temporary increases and decreases in CA 15-3 that do not match with the patient’s progress. Usually, your doctor will wait a few weeks after starting treatment to begin monitoring CA 15-3 concentrations.
I have a strong family history of breast cancer. Shouldn't I be screened for CA 15-3?
CA 15-3 is not recommended as a screening tool to detect early breast cancer. Increases in CA 15-3 may be due to other causes, and negative results do not accurately predict the absence of cancer. It should only be used after breast cancer has been diagnosed.
What can I do to lower my CA 15-3?
There is nothing you can do directly to lower your CA 15-3 concentration. It is not a risk factor like cholesterol that can be lowered through dietary restrictions and exercise. It is a reflection of what is going on in your body. CA 15-3 may rise with tumour growth and fall with treatment, or it may be mildly elevated and stable in a benign condition.