Also Known As
Cancer Antigen 15-3
Formal Name
Cancer Antigen 15-3
This article was last reviewed on
This article waslast modified on 29 January 2019.
At a Glance
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?


On average it takes 7 working days for the blood test results to come back from the hospital, depending on the exact tests requested. Some specialist test results may take longer, if samples have to be sent to a reference (specialist) laboratory. The X-ray & scan results may take longer. If you are registered to use the online services of your local practice, you may be able to access your results online. Your GP practice will be able to provide specific details.

If the doctor wants to see you about the result(s), you will be offered an appointment. If you are concerned about your test results, you will need to arrange an appointment with your doctor so that all relevant information including age, ethnicity, health history, signs and symptoms, laboratory and other procedures (radiology, endoscopy, etc.), can be considered.

Lab Tests Online-UK is an educational website designed to provide patients and carers with information on laboratory tests used in medical care. We are not a laboratory and are unable to comment on an individual's health and treatment.

Reference ranges are dependent on many factors, including patient age, sex, sample population, and test method, and numeric test results can have different meanings in different laboratories.

For these reasons, you will not find reference ranges for the majority of tests described on this web site. The lab report containing your test results should include the relevant reference range for your test(s). Please consult your doctor or the laboratory that performed the test(s) to obtain the reference range if you do not have the lab report.

For more information on reference ranges, please read Reference Ranges and What They Mean.

What is being tested?

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.

Accordion Title
Common Questions
  • 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?

    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.

  • 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.