How is it used?When is it ordered?What does the test result mean?Is there anything else I should know?
CA 15-3 is not sensitive or specific enough to be considered useful as a tool for cancer screening. Its main use is as a
tumor marker to monitor a patient’s response to
breast cancer treatment and to watch for breast cancer recurrence. CA 15-3 can only be used as a marker if the cancer is producing elevated amounts of it; however, since only a small percent of women with localized breast cancer have increased CA 15-3, it may still be able to be used later as a marker. CA 15-3 sometimes may also be used to give a doctor a general sense of how much cancer may be present.
CA 15-3 may be ordered along with other tests, such as
estrogen 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 initially elevated, then it may be used to monitor treatment and, if repeated on a regular basis, to detect recurrence. CA 15-3 is usually not done 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 (amount of
tumor present). The level tends 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.
Mild to moderate elevations of CA 15-3 also are seen in a variety of 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 do not ensure that a patient does not have cancer. It may be too soon in the disease for elevated levels to be detected. In addition, 25% to 30% of individuals with advanced breast cancer have tumors that do not shed 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. There have been instances of transient (temporary) increases and decreases in CA 15-3 that do not correlate with the patient’s progress. Usually, your doctor will wait a few weeks after starting treatment to begin monitoring CA 15-3 levels.
