Your doctor may order blood tests for cancer/tumor markers to detect cancer activity in the body. Proteins and circulating tumor cells are two types of markers that can be measured. A cancer tumor often produces a specific protein in the blood that serves as a marker for the cancer. Circulating tumor cells are cells that break off from the cancer and move into the blood stream. Protein markers and circulating tumor cells can be measured with simple blood tests.
Blood marker tests may be done before treatment, to help diagnose the breast cancer and determine whether it's moved to other parts of the body; during treatment, to assess whether the cancer is responding; and after treatment, to see if the cancer has come back (recurrence).
Examples of 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.
- Circulating tumor cells: cells that break off from the cancer and move into the blood stream. High circulating tumor cell counts may indicate that the cancer is growing. The CellSearch test has been approved by the U.S. Food and Drug Administration to monitor circulating tumor cells in women diagnosed with metastatic breast cancer.
Some doctors use marker test results as early indicators of breast cancer progression (the cancer getting worse) or recurrence. 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.
While breast cancer blood marker tests are promising, they're not absolutely conclusive. When a breast cancer blood marker test comes back negative, it doesn't necessarily mean you're free and clear of breast cancer. And a positive result doesn't always mean that the cancer is growing. These tests may help with diagnosis, but using cancer marker tests to find metastatic breast cancer hasn't helped improve survival yet.
When deciding if you should get tested for breast cancer blood markers, there are some things you may want to consider:
- cost — the tests can be expensive
- anxiety — not just from an elevated blood marker, but by all the tests you may need to find out what's causing the marker to go up
Talk to your doctor about the possible benefits and risks of blood marker testing in your unique situation.