The cancer antigen CA-15.3 is used to monitor response to breast cancer treatment and disease recurrence. They are used along with other clinical evaluations and tests, such as estrogenic and progesterone receptors, Her2/neu and gene expression test for breast cancer to evaluate a person's breast cancer. CA 15.3 gives general sense to oncologists of how much cancer may be present. CA 15.3 can only be used as a marker if the cancer is producing elevated amounts of it, so this test is not useful for all people with breast cancer. The reference range of serum CA 15.3 is less than 30 U/mL