CA 15-3 – tumour marker for monitoring breast cancer

CA 15-3 is a tumour marker measured in blood and used primarily in women already diagnosed with breast cancer: to monitor treatment response and detect disease recurrence. It is unsuitable for screening healthy women or early breast cancer diagnosis because it may be raised without cancer and is usually normal in early-stage cancer.

Who the test is for

• women with confirmed breast cancer before treatment, as a baseline against which later results are compared,
• women being treated for advanced (metastatic) disease, alongside imaging to assess whether treatment is working,
• women after treatment to monitor possible recurrence, if their oncologist decides to do so,
• women with mildly raised CA 15-3 without a cancer diagnosis, when a doctor decides to repeat measurement.

What CA 15-3 is and what it shows

CA 15-3 (cancer antigen 15-3) is the glycoprotein MUC1 released into blood by glandular tissue cells, including breast cells. In breast cancer, particularly when it has spread to other organs, more of this antigen can enter the blood.

CA 15-3 is not specific to breast cancer: it can also rise in other diseases and remains normal in some breast cancer patients. According to the European Group on Tumour Markers (EGTM), it is raised in 50–70 % of patients with distant metastases, while it is usually normal in early disease. It is therefore always interpreted alongside examination, imaging and other findings.

CA 15-3 is used when breast cancer is confirmed. Guidelines differ regarding monitoring after completed treatment: EGTM recommends regular measurements, while the American Society of Clinical Oncology (ASCO) and European Society for Medical Oncology (ESMO) do not recommend routine marker measurement in asymptomatic women. Your oncologist decides whether and how often CA 15-3 is monitored.

CA 15-3 is not a test for early detection of breast cancer. Mammography serves that purpose. The National Breast Cancer Early Detection Programme covers women aged 49 to 70, who receive a letter inviting them for mammography every two years. If you notice a breast change, see a doctor (more in the article Early symptoms of breast cancer). Diagnosis is made through examination, imaging and biopsy, not a tumour marker.

Save with a panel

Test CA 15-3 is also included in this panel.

Tumour marker panel – womenCEA, CA 19-9, CA125, CA 15-3Price of individual tests: 79.00€71.00€Details ›

Preparation and sample

A venous blood sample is taken. No special preparation or fasting is needed unless other tests requiring it, such as glucose or blood lipids, are performed the same day.

If you take biotin (for example hair and nail supplements), mention it during blood collection.

How to interpret the result

The upper reference limit depends on the method and is most often between 25 and 32 U/ml. Some laboratories report results in kU/L, which is numerically the same. The limit printed on your report is authoritative.

There are two important limitations:

• False-negative result. A normal value does not rule out breast cancer. CA 15-3 remains within range in early-stage cancer and in some women with advanced disease.
• False-positive result. A raised value does not mean you have cancer. CA 15-3 can rise in benign breast and ovarian conditions, liver diseases such as hepatitis and cirrhosis, autoimmune diseases and other malignancies, such as lung, pancreatic, ovarian and colorectal cancers. Because the reference limit is based on values in healthy people, a small proportion of healthy people also have a result above it.

In women being treated for breast cancer, a doctor considers the trend over several measurements rather than one result. A fall usually accompanies a good treatment response, while a rise on consecutive measurements may suggest progression. In the first weeks of new therapy, the value can rise temporarily even when treatment is effective, so such a rise is checked by repeat measurement.

There is no threshold above which CA 15-3 alone confirms metastases. High values are more common in advanced disease, but metastases are established by imaging and, when necessary, biopsy.

How to arrange testing

You can have blood taken without an appointment or referral at one of our branches across Croatia (listed under Contact). Prices for all tests and panels are available in the service price list.

CA 15-3 is also part of the Women’s marker panel, which also includes CEA, CA 19-9 and CA 125. The panel is not a screening test for healthy women either. What individual markers can and cannot show is described in the article Tumour markers.

Frequently asked questions

Can a CA 15-3 test check whether I have breast cancer?

No. A normal result does not rule out cancer and a raised result does not mean you have it, so testing would not provide a reliable answer. Mammography and, at a doctor’s discretion, breast ultrasound are used for early detection.

My CA 15-3 is mildly raised and I have no cancer diagnosis. What now?

A mildly raised value is not itself a diagnosis. It may be caused by one of the benign conditions listed above, and a small proportion of healthy people have a value slightly above the limit. Such a result is interpreted alongside symptoms and other findings, and measurement is often repeated after several weeks.

How often is CA 15-3 monitored?

There is no universal schedule. During metastatic disease treatment, measurements are usually coordinated with treatment cycles and imaging checks; after completed treatment they depend on the oncologist’s assessment.

Why do results differ between laboratories?

Laboratories use different methods, and results from different methods are not directly comparable. If monitoring CA 15-3 over a longer period, always use the same laboratory.