The FDA approved the CA 27.29 blood test in June 1996. It is the first and only blood test that is specific to breast cancer. (The two other blood tests that oncologists may recommend for women with breast cancer, the CA 15-3 and the CEA, are tumor marker tests that are used in breast and other cancers.) The CA 27.29 test measures the level of CA 27.29 antigen, which is found in the blood of breast cancer patients. As breast cancer progresses, the level of CA 27.29 antigen in the blood rises. In theory, by monitoring CA 27.29 test results oncologists can determine if the cancer has spread to other parts of the body, which is called metastasis. [Important point: If breast cancer metastasizes to the liver, it does not mean you have liver cancer. It means you have breast cancer cells in your liver, and the treatment used would be treatment for breast cancer, not treatment for liver cancer.]
Unfortunately, the CA 27.29 test is not as reliable as we initially hoped it would be. In statistical terms, it is neither "specific" nor "sensitive" enough to accurately determine if metastasis has occurred. What does that mean?
If a test for metastasis is highly sensitive, it will be good at finding those women who have metastasis and it will produce very few false negatives (women who are told they have negative results when they really don't). A test needs to be highly sensitive to rule out disease. In other words, when a test is highly sensitive, if a woman tests negative it means she does not have metastasis.
If a test for metastasis is highly specific, it will be good at finding those women who do not have metastasis and it will produce very few false positives (women who are told they have metastasis when they really don't). In other words, when a test is highly specific, if a woman tests positive it means that metastasis is indeed present.
Since it is not highly sensitive or specific, the CA 27.29 test can go up for reasons other than metastasis, resulting in false positives, and it may not go up when there is metastasis, resulting in false negatives. The CA 27.29 test has been proven to be helpful in following increases in metastasis in women who have already been found to have metastatic disease, allowing doctors to better adjust treatment regimens.
In addition to having the CA 27.29 test, your oncologist may recommend that you have the CEA and CA 15-3 tumor marker tests done as well. Neither of these tests is highly sensitive or highly specific either. If you choose to have any of these tests done it should be with the knowledge that there is currently no test or scan that can reliably tell us whether a small number of breast cancer cells have gotten into, and have begun growing in, other parts of the body, and that the information you receive may not be accurate.
Should you have the CA 27.29 test done? The American Society of Clinical Oncology recommends against routine testing of markers after a breast cancer diagnosis. Some oncologists recommend that women have this test every three to six months with the hope that they will find metastasis early. The problem is that there is no evidence that finding metastases by a blood test before a woman has symptoms will improve her survival or quality of life. The treatment of metastatic disease is aimed at reducing symptoms and putting the woman into remission. It is hard to improve symptoms if a woman does not have any. Most women whose breast cancer has metastasized do not show any symptoms until the disease is quite extensive. Symptoms of metastatic disease include bone pain, shortness of breath, lack of appetite and weight loss, and neurological symptoms like pain or weakness or headaches.
There are a series of tests that can help find large amounts of cancer cells in other parts of the body. These are called staging tests (this is not the same as the stages of breast cancer), and include chest X-rays, which can find cancer in the lungs, blood tests that can determine if the cancer has spread to the liver, and bone scans, which can help ascertain if the cancer has spread to the bone. CT scans are also used to detect the spread of cancer to the liver, the lungs, a certain area of bone, or even your brain. Like the blood tests, though, these tests are not good at finding small numbers of cancer cells.
Ultimately, the only way to determine whether having routine CA 27.29 testing is right for you is to think about how you want to handle the aftermath of your breast cancer treatment and whether a test that has limitations will be helpful for you. Some women find reassurance in having the CA 27.29 test done; others find the thought of having the test stressful and choose to not have it done. There is no "right" choice. If you do decide to have the test done, here are a few things you should know:
a normal CA 27.29 level is usually less than 38 to 40 U/ml (units/milliliter), depending on where the lab test is done
because anything under 40 is considered normal, you shouldn't worry if it's 20 one time and then 30 another time
just because the test result is higher than 40 it doesn't mean your cancer has spread. Endometriosis, ovarian cysts, first-trimester pregnancy, benign breast disease, and kidney and liver disease are just some of the noncancerous conditions that can raise your CA 27.29 level.