The normal range of the tumor marker 15-3 (also known as cancer antigen 15-3) is less than or equal to 30 units per milliliter.
The blood test is used to monitor the treatment of breast cancer to see if it has returned or has spread.
CA15-3 is an antigen that stimulates the immune system. Higher than normal levels of CA15-3 are not always due to cancer.
Not all labs use the same procedure to test blood, so the results can sometimes be different. Noncancerous diseases of the breast, ovary, and liver also increase antigen levels.
If the results improve, additional information is collected to determine the cause.