The CA 15-3 test measures the level of Cancer Antigen 15-3, a protein produced by normal breast cells and in higher amounts by breast cancer cells. CA 15-3 is a tumor marker that is shed into the bloodstream by cancer cells, making it detectable through a blood test.
This test is primarily used to monitor the progression of breast cancer and evaluate the response to breast cancer treatment. It is not generally used as a screening test for breast cancer, as elevated levels can also be seen in other cancers (lung, ovarian, liver) and in some benign conditions such as liver disease, benign breast disease, and autoimmune conditions.
