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.
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.
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.
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.
This article was last reviewed on December 4, 2012. | This article was last modified on December 13, 2013.
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