How is it used?
CA 15-3 is not or 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 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 breast cancer patients.
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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 detect 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.
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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.
Mild to moderate elevations of CA 15-3 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 non-cancerous conditions tend to be stable over time.
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 25% to 30% of individuals with advanced breast cancer whose tumors do not shed CA 15-3.
Increasing concentrations of CA 15-3 over time may indicate that a patient is not responding to treatment or that the cancer is recurring.
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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.
CA 15-3 can be elevated in malignancies other than breast cancer, including lung, pancreatic, ovarian, liver, and colorectal cancers.
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