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CA 15-3


At a Glance

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?

None

The Test Sample

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.

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

No test preparation is needed.

The Test

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.



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