Summary

• CA125 is a cancer antigen, also called a tumour marker.
• Tumour markers are substances that can be made by cancer cells or by normal cells in response to cancer.
• Ovarian cancer can cause high levels of CA125 in the blood.
• Measuring CA125 in a blood sample can help monitor treatment for ovarian cancer and to make sure the cancer has not come back after treatment.
• It cannot be used to diagnose ovarian cancer because other conditions also cause CA125 levels to rise.

What is CA125 (cancer antigen 125)?

CA125 is a test that is used to monitor ovarian cancer. It is what is called a tumour marker test. These look for substances made by cancer cells or released by the body in response to cancer. By measuring levels of these substances in the blood, tumour marker tests can be used to help monitor cancer treatment.

CA125 is a fragment of the MUC16 protein. MUC16 is a normal protein that your body makes every day. It belongs to a group of proteins that help protect and lubricate body surfaces. It is mainly made by cells in the lining (serosa) of certain organs, especially the ovaries, uterus, cervix, peritoneum (the membrane that lines the inside of your abdomen and pelvis and covers many of your organs) and the lung cavity.

When these tissues are inflamed, stretched, damaged or are rapidly growing, they make more MUC16. This means that CA125 is the marker of irritation or activity of tissues that normally produce the protein MUC16. CA125 increases whenever these lining cells are active and this is why CA125 can be raised in non-cancerous conditions.

When cells in the ovaries become cancerous large amounts of CA125 can be found in the bloodstream, especially when the tumour involves the surface of the ovaries or nearby linings.

The CA125 test cannot be used to detect or diagnose ovarian cancer because it is not specific to ovarian cancer. It is raised in many non-cancerous conditions as well as ovarian and several other cancers.

But by measuring whether levels of CA125 rise or fall, it can be used to see if treatment for ovarian cancer is working or not and check to see if a cancer is coming back.

Why get tested?

CA125 is used to monitor treatment for ovarian cancer and to make sure the cancer has not come back after treatment. It cannot be used to diagnose ovarian cancer because other conditions also cause higher levels of CA125 in the blood. These include endometriosis, fibroids, pelvic inflammatory disease, pregnancy and any condition causing fluid in the abdomen (ascites) such as liver disease. CA125 levels naturally rise and fall during menstruation and in pregnancy.

The test is used to track changes in CA125 levels. This can show if your treatment for ovarian cancer is working. If you are diagnosed with ovarian cancer your doctor will measure a baseline CA125 level to compare against future measurements.

After your surgery and during treatment (such as chemotherapy or PARP inhibitor) CA125 testing will be used at intervals to monitor your response. CA125 will also be measured from time to time after your treatment is completed to catch any early signs of the cancer’s return. Your results will be considered along with the results of a pelvic ultrasound or CT scan.

Diagnosing ovarian cancer

When ovarian cancer is suspected based on your symptoms, the doctor will order several imaging tests and tumour markers that can support the assessment. These markers cannot make a diagnosis on their own but can be used to monitor therapy. CA125 is the main tumour marker used for ovarian cancer. In addition, if you are diagnosed with ovarian cancer, you may be offered genetic testing for BRCA1 and BRCA2.

Having the test

Sample

Blood.

Any preparation?

None.

Your results

CA125 is high in about 80 per cent of ovarian cancer cases. The more advanced the ovarian cancer, the higher the levels of CA125.

Questions to ask your doctor

The choice of tests your doctor makes will be based on your medical history and symptoms. It is important that you tell them everything you think might help.

You play a central role in making sure your test results are accurate. Do everything you can to make sure the information you provide is correct and follow instructions closely.

Talk to your doctor about any medications you are taking. Find out if you need to fast or stop any particular foods or supplements. These may affect your results. Ask:

• Why does this test need to be done?
• Do I need to prepare (such as fast or avoid medications) for the sample collection?
• Will an abnormal result mean I need further tests?
• How could it change the course of my care?
• What will happen next, after the test?

More information

Pathology and diagnostic imaging reports can be added to your My Health Record. You and your healthcare provider can now access your results whenever and wherever needed.

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