Blood Marker Tests

Your doctor may order blood tests for “cancer markers” or “tumor markers” to detect possible cancer activity in the body. When cancer is present, it often will produce a specific protein in the blood that serves as a “marker” for the cancer. Blood marker tests may be done before treatment, to help diagnose the breast cancer and determine whether it may have traveled to other parts of the body; during treatment, to assess whether the cancer is responding; and after treatment, to monitor for a possible recurrence of the cancer.

Examples of blood markers your doctor may test for include:

• CA 15.3: used to find breast and ovarian cancers
• TRU-QUANT and CA 27.29: may mean that breast cancer is present
• CA125: may signal ovarian cancer, ovarian cancer recurrence, and breast cancer recurrence
• CEA (carcinoembryonic antigen): a marker for the presence of colon, lung, and liver cancers. This marker may be used to determine if the breast cancer has traveled to other areas of the body.

Some doctors rely on markers as early indicators of breast cancer progression (the cancer getting worse) or recurrence (the cancer coming back). They may use this information to make decisions about when to change therapies — if current treatment does not appear to be working — or to start treatment for recurrence. If you have an elevated marker, your doctor may check that marker periodically to assess your response to chemotherapy or other treatments.

The blood marker tests used for breast cancer are not as reliable as some other blood marker tests. For example, a blood marker test for breast cancer that returns a negative result does not carry the same level of certainty that you are cancer-free as would a negative result for prostate-specific antigen (PSA), a blood marker test for prostate cancer. If a man’s PSA is negative, he can be assured with a fairly high degree of certainty that he does not have prostate cancer. However, when a blood marker test for breast cancer comes back negative, it may not necessarily mean you’re free and clear of breast cancer. At the same time, an elevated test result for breast cancer blood markers does not definitely mean that the cancer is progressing or recurring. Although these tests may be helpful for diagnosis, the use of cancer markers to find metastatic cancer has not yet translated into better survival for people with breast cancer.

There are other things to take into consideration when deciding whether to get tested for breast cancer blood markers. Cost is one — the tests can be expensive. Another thing to think about is the anxiety caused not just by an elevated blood marker, but by all of the tests that may be needed to try to find out what is causing the marker to go up.

Talk to your doctor about the possible advantages and disadvantages of blood marker testing in your particular situation.