CA 15-3 Test
Note: this site is for informational purposes only. To view test results or book a test, use the NHS app in England or contact your GP.
The CA 15–3 test measures CA 15–3 levels in a blood sample to detect a protein released by some breast cancer cells. It is used to monitor response to treatment and detect recurrence or progression of breast cancer rather than to screen for the disease.
Why get tested?
To monitor the response to treatment of breast cancer and to watch for recurrence of the disease
When to get tested?
When you have been or are being treated for breast cancer
Sample required?
A blood sample taken from a vein in your arm
Test preparation needed?
None
Common questions
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.
CA 15–3 may be requested during follow-up following surgical removal of a breast cancer. It may be also requested when a patient with advanced breast cancer is receiving treatment. Changes in the concentration of CA 15–3 may indicate if a tumour is responding to treatment.
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.
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.
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.
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.