Cancer Antigen 15-3

Other names: CA 15-3

Cancer Antigen 15-3 is a product of the breast cells; it is a protein which is shed by tumour cells in the breast. Levels of CA 15-3 are higher if a person has breast cancer.

When is the test used?

The test is used to monitor the progress of a patient who has been diagnosed with breast cancer; the test assesses the levels of CA 15-3, which is a protein shed by tumour cells in the breast. The test can measure the levels of CA 15-3 as the patient undergoes treatment. The test may also be used after the completion of treatment to test for early warning signs that the cancer has returned.

How is the test performed?

The test is done by taking a sample of blood from a vein in the arm; usually doctors use a vein on the inside of the elbow, as these veins are usually more prominent and easier to get the needle into in this area of the arm. Once the needle has been inserted, the blood will start to collect in a syringe, which is attached to the needle. When the sample has been collected, it will be bottled, labelled and sent away to the laboratory for analysis.

What does the result show?

The levels of CA 15-3 are higher if a patient has breast cancer; in general, the higher the level, the more advanced the cancer. If levels are very high, this usually means that the cancer has spread to other organs (metastatic cancer).

Slightly higher levels of CA 15-3 may be seen in other health conditions, including liver and pancreatic cancer and liver cirrhosis.

If the results are negative, this does not necessarily mean that the patient does not have breast cancer because around 15-30 percent of patients with breast cancer do not produce the CA 15-3 protein.

Doctors will usually wait a few weeks to do the test after a patient has started treatment for breast cancer; this is because the levels may rise and fall to start with so the result of the test may not be accurate during this period of time.

Specific Blood Tests

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