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 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 , 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 amount of 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, , and 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 can not 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?
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.