Patient Test Information

CA 15-3

Also known as:

CA-Breast; Cancer Antigen-Breast

Formal name:

Cancer Antigen 15-3

Related tests:

CA 27.29; Tumor Markers; CEA; Her2/neu; Estrogen/Progesterone Receptor Status; Gene Expression Tests for Breast Cancer

Why Get Tested?

To monitor the response to treatment of invasive breast cancer and to help watch for recurrence of the disease

When to Get Tested?

When you have been or are being treated for invasive breast cancer

Sample Required?

A blood sample drawn from a vein in your arm

Test Preparation Needed?


How is it used?

CA 15-3 is not sensitive or specific enough to be considered useful as a tool for cancer screening. Its main use is to monitor a person's response to breast cancer treatment and to help watch for breast cancer recurrence. CA 15-3 is sometimes ordered to give a doctor a general sense of how much cancer may be present (the tumor burden). CA 15-3 can only be used as a marker if the cancer is producing elevated amounts of it, so this test will not be useful for all people with breast cancer.

When is it ordered?

CA 15-3 may be ordered along with other tests, such as estrogen and progesterone receptors, Her2/neu, and gene expression tests for breast cancer, when advanced breast cancer is first diagnosed to help determine cancer characteristics and treatment options. If CA 15-3 is initially elevated, then it may be ordered periodically to monitor the effectiveness of treatment and to help watch for recurrence. CA 15-3 is usually not ordered when breast cancer is detected early, before it has metastasized, because levels will not be elevated in the majority of early cancers.

What does the test result mean?

In general, the higher the CA 15-3 level, the more advanced the breast cancer and the larger the tumor burden. CA 15-3 concentrations tend to increase as the cancer grows. In metastatic breast cancer, the highest levels of CA 15-3 often are seen when the cancer has spread to the bones and/or the liver.

Increasing concentrations of CA 15-3 over time may indicate that a person is not responding to treatment or that the cancer is recurring.

Normal CA 15-3 levels do not ensure that a person does not have localized or metastatic breast cancer. It may be too soon in the disease for elevated levels of CA 15-3 to be detected or the person may be one of the 20% to 25% of individuals with advanced breast cancer whose tumors do not shed CA 15-3.

Mild to moderate elevations of CA 15-3 are seen in a variety of conditions, including cancer of the lung, pancreas, ovary, prostate, and colon as well as cirrhosis, hepatitis, and benign breast disorders and in a certain percentage of apparently healthy individuals. The CA 15-3 elevations seen in non-cancerous conditions tend to be stable over time.

Is there anything else I should know?

Levels of CA 15-3 are not usually measured immediately after breast cancer treatment begins. There have been instances of transient increases and decreases in CA 15-3 that do not correlate with the person's progress. Usually, the doctor will wait a few weeks after starting treatment to begin monitoring CA 15-3 levels.

What is being tested?

Cancer antigen 15-3 (CA 15-3) is a protein that is produced by normal breast cells. In many people with cancerous breast tumors, there is an increased production of CA 15-3 and the related cancer antigen 27.29. CA 15-3 does not cause cancer; rather, it is shed by the tumor cells and enters the bloodstream, making it useful as a tumor marker to follow the course of the cancer.

CA 15-3 is elevated in only about 10% of women with early localized breast cancer but is elevated in about 80% of those with metastatic breast cancer.

CA 15-3 may also be elevated in healthy people and in individuals with other cancers (e.g., colon, lung, pancreas, ovary, or prostate malignancies) or certain conditions (e.g., 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.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.

  1. Should I have a test for CA 27.29 in addition to the CA 15-3 test?

    No. Although it has a different name, the CA 27.29 test measures the same protein as CA 15-3 and is used in the same way. It can be used instead of CA 15-3, but you don't need both tests.

  2. 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. It is not specific or sensitive enough to detect early breast cancer. Elevations in CA 15-3 may be due to other causes, and a normal value does not ensure that you do not have cancer. As a rule, it should only be used after breast cancer has been diagnosed.

  3. What can I do to lower my CA 15-3?

    There is nothing you can do directly to lower your CA 15-3 level. It is not a risk factor that can be lowered through, for example, lifestyle changes. It is a reflection of what is going on in your body. CA 15-3 may rise with tumor growth and fall with treatment, or it may be mildly elevated and stable in a benign condition.