CA15-3 (Cancer Antigen 15-3) is a tumor marker used to monitor certain cancers, especially breast cancer. It is found on the surface of many types of cancer cells and shed into the blood stream. It is used to monitor advanced, ie metastatic, cancer[1].
Elevated CA15-3, in conjunction with alkaline phosphatase (ALP), was found to be associated with an increased chance of early recurrence in breast cancer.[2]