Cancer antigen 15-3
To monitor the response to treatment of breast cancer and to watch for recurrence of the disease
When you have been or are being treated for breast cancer
A blood sample drawn from a vein in your arm
Cancer antigen 15-3 (CA 15-3) is a normal product of breast cells. Levels of CA 15-3 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 elevated in about 30% of women with localised breast cancer and 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.
A blood sample is obtained by inserting a needle into a vein in the arm.
No test preparation is needed.
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 along with other tests, such as oestrogen and progesterone receptors, Her2/neu, and BRCA-1 and BRCA-2 genetic testing, when advanced breast cancer is first diagnosed to help determine cancer characteristics and treatment options.
If CA 15-3 is elevated, then it may be used to monitor treatment and, if repeated on a regular basis, to detect recurrence. CA 15-3 is not always measured when breast cancer is detected early, before it has metastasised, because levels will not be elevated in the majority of early cancers.
In general, the higher the CA 15-3 level the more advanced the breast cancer and the larger the amount of tumour present. The level tends to increase as the cancer grows. In metastatic breast cancer (cancer that has spread to other organs), the highest levels 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.
Negative CA 15-3 levels 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.
Levels of CA 15-3 are not usually taken immediately after breast cancer treatment begins because there have been instances of temporary increases in CA 15-3 that do not match with the patient’s progress. Your doctor may wait a few weeks after starting treatment to begin monitoring CA 15-3 levels.
Tumour markers, CEA, HER-2/neu, hormone receptor status
Conditions: Breast cancer
RCPA Manual: tumour markers
Healthdirect Australia: Breast cancer
Cancer Council: Breast cancer
Last Review Date: September 17, 2022