What Should You Know About Tumor Markers?

Patient Expert
Medically Reviewed

As a breast cancer survivor, you may have heard of "tumor markers." What exactly are tumor markers? How accurate are they? And why do some doctors disregard them, while others set great store by them?

Q. At my last appointment, my oncologist mentioned tumor markers, and I didn't know what he was talking about. What are they?

A. The term "tumor markers" covers a wide range of territory. Basically, a tumor marker is a substance sometimes produced by cancer and also often non-cancerous tissue. This is generally a protein, or part of a protein; though sometimes it can be a hormone.

Q. How do tumor markers form?

A. Usually, they're the result of quickly dividing cancer cells, which "shed" certain proteins into your blood. A high level of these specific proteins may indicate the presence of cancer cells - or not. (But we'll get to that later.) Tumor markers may be found in the tumor itself, as well as in the blood.

Q. So, how would I be tested for tumor markers?

A. A blood test is the usual way to check for breast cancer tumor markers. Blood is combined with manmade antibodies that will react with the tumor marker protein, if it's present.

Q. Are there a lot of different tumor markers I need to watch out for?

A. No, not really. Certain markers are tracked in certain situations; depending on your diagnosis, there may not be any tumor markers to watch for; or your doctor may get a baseline before treatment, with a comparison afterwards, to see if the treatment was effective; or you may have your markers tracked consistently, as in the case of metastatic cancer.

Let's take a look at the various tumor marker tests, and how they're used:

At diagnosis: During analysis of your tumor, the pathologist will test for hormone receptivity (estrogen and progesterone, a.k.a. ER/PR); and for the presence of the HER2-neu protein.

Other tests might include one for the presence of ki-67 protein; an Oncotype-DX test, to test for elevated levels of 21 different proteins; and the uPA and PAI-1 tests, similar to the Oncotype test.

The ER/PR test determines if your cancer needs hormones to grow; if it does, you'll be able to take hormone therapy drugs to help prevent recurrence. The HER2-neu test predicts how aggressive the cancer is. A HER2+ result means you'll likely be responsive to Herceptin, a drug that helps prevent recurrence.

During treatment: CA 27.29 is a test sometimes used during active treatment. Your doctor will test for its presence before treatment starts, then at intervals during treatment. If your CA (cancer antigen) 27.29 level rises, the treatment may need to be adjusted; if it falls, it shows that the treatment is working.

After treatment, and long-term: There are three types of tumor marker tests used long-term, either to monitor how fast cancer is progressing in women with stage 4 (metastatic) cancer; or to help detect recurrence. The above-mentioned CA 27.29 test; the CEA test; and the CA 15-3 test are all tumor marker tests you may hear about, once you've finished treatment.

Q. So, I might be tracking tumor markers for years to come?

A. Well, this is where it gets a little murky.

If you develop metastatic breast cancer, then tumor marker tests will be a regular part of your treatment. Your doctor may choose to use all three of the tests mentioned above, or not; CA 15-3 is the test most commonly used in women with metastatic cancer.

If you don't have metastatic cancer, but were treated for an aggressive cancer, your doctor may choose to monitor your tumor markers regularly. For instance, women treated for inflammatory breast cancer, a particularly aggressive type, will often have regular tumor marker tests.

If your cancer wasn't classified as particularly aggressive, you may or may not be tested regularly for tumor markers. Some doctors think these tests are helpful; some don't.

Q. Why the disagreement? Why don't they just go ahead and do the tests? Don't tumor markers mean cancer is present somewhere in your body?

A. Actually, tumor markers in and of themselves don't indicate the presence of cancer. There are many other reasons why your cells may shed these certain proteins, including other diseases (hepatitis, pelvic inflammatory disease); pregnancy and lactation; endometriosis, and fibroadenomas. Tumor markers must be seen in the context of other signs of cancer, to be truly indicative of its presence.

A tumor marker test may come back high as the result of conditions at the lab where the test was performed; and a perfectly healthy person may show higher than normal levels of tumor marker proteins. In addition, some patients with active cancer produce no tumor markers at all.

Bottom line: tumor markers aren't a particularly reliable way to spot an early recurrence of cancer. In addition, studies have shown that detecting a recurrence in its earliest stages, as a result of a tumor marker test, has no bearing on survival time, or quality of life. Women whose recurrence was caught later had the same results as women where it was detected earlier.

And that, in a nutshell, is why the majority of doctors don't monitor tumor markers in breast cancer survivors (unless their initial cancer was particularly aggressive; or it's metastasized). A tumor marker test is yet another test to be administered (time, money, and inconvenience); and it may or may not be accurate.

Even if it's accurate, it doesn't seem to make any difference in outcome if the recurrence is caught very early; or later, when other symptoms (a new lump, pain, evidence of liver dysfunction) are present.

Nevertheless, it's good to ask your doctor about tumor marker tests. You'll want to know which ones have already been performed (e.g., ER/PR, HER2-neu, Oncotype, etc.); and whether s/he recommends any further tests, going forward.