By Dr. Kathleen Ruddy

The cancer antigen 27.29 test is a blood test used to monitor patients with breast cancer. Cancer antigen 27.29 is the only antigen blood test specific to breast cancer and it measures the levels of cancer antigens found in the blood. If your doctor wants you to have this test, it is important to understand what it is and how it works. There is some disagreement about the usefulness of this particular test.

What does the Cancer Antigen 27.29 Test Measure?

Cancer Antigen 27.29 or CA 27.29 is a protein or tumor marker found in the blood. It indicates the presence of breast cancer in the patient who is tested. The amount of this protein in the blood will be higher if the cancer is more progressed.

When is the Cancer Antigen 27.29 Test Ordered?

Your doctor may order the test as soon as you are diagnosed with breast cancer, in order to get a sense of whether it has metastasized, or spread to other parts of the body. This test may also be ordered as you progress through the treatment for breast cancer, in order to see if the levels are lower, which would indicate that the treatment is working.


If you are a younger woman and you have a suspicious lump in your breast, be persistent in expressing your concerns about it to your physician. Because breast cancer is more common in women over 40, doctors will often dismiss the concerns of younger women without doing the appropriate tests.

What do the Results of the Cancer Antigen 27.29 Mean?

It was initially thought that higher levels of CA 27.29 meant that the breast cancer has spread to other parts of the body instead of being simply confined to breast tissue or instead of being completely removed by treatment.

Is the Cancer Antigen 27.29 Test Reliable?

Unfortunately, recent scientific research suggests that the CA 27.29 test is not very specific or reliable. This means that it often results in false negatives, as a result of which women are told they don’t have metastasis, when they actually do, and that it often results in false positives, too, as a result of which women are told that the cancer has indeed spread when in fact it has not.

Should You Have the Cancer Antigen 27.29 Test?

Some cancer specialists do recommend this test every three to six months after the initial diagnosis of breast cancer, with the hope that they will be able to use it to catch metastasis early. But the American Society of Clinical Oncology recommends that patients diagnosed with breast cancer should not be tested for these markers because the results of these tests are so unreliable as to be completely unhelpful.

In conclusion, one of the many tests you may have to undergo when you are diagnosed with breast cancer is the Cancer Antigen 27.29 blood test. This test reveals the levels of certain protein markers of tumors in your blood. In the past, it was thought that high levels of CA 27.29 indicated that the breast cancer has spread throughout the entire body. Recently though, it has been demonstrated that this test is unreliable and may give patients both false negatives and false positives.

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