Patient Test Information


Also known as:

CA 125 Tumor Marker

Formal name:

Cancer Antigen 125

Related tests:

Tumor Markers, BRCA-1 and BRCA-2, Human Epididymis Protein 4 (HE4)

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Why Get Tested?

To monitor treatment for ovarian cancer or to detect recurrence; sometimes to evaluate a lump located in the pelvic area (pelvic mass); not recommended for screening asymptomatic women but sometimes ordered to help detect early ovarian cancer in those identified as being at high risk

When to Get Tested?

Before starting therapy for ovarian cancer and at intervals during and after treatment; sometimes when you have a pelvic mass or are at a high risk for developing ovarian cancer

Sample Required?

A blood sample drawn from a vein in your arm

Test Preparation Needed?


How is it used?

Thumbnail diagram of the cervix

Cancer Antigen 125 (CA-125) is a tumor marker primarily used to monitor therapy during treatment for ovarian cancer. CA-125 is also used to detect whether cancer has come back after treatment is complete. A series of CA-125 tests that shows rising or falling concentrations is often more useful than a single result.

CA-125 is sometimes used along with transvaginal ultrasound to test and monitor women who have a high risk for ovarian cancer but who do not yet have the disease. The most significant risk factor for ovarian cancer is an inherited genetic mutation in one of two genes: breast cancer gene1 (BRCA1) or breast cancer gene 2 (BRCA2). Other risk factors are family history, increasing age, reproductive history and infertility, use of hormone replacement therapy, and obesity.

Sometimes a CA-125 test may be ordered along with a transvaginal ultrasound to help investigate a lump in woman's lower abdominal area (pelvic mass.)

The test is not used, however, to screen women for ovarian cancer because it is non-specific. The U.S. Preventive Services Task Force recommends against screening women for ovarian cancer. This recommendation applies to asymptomatic women but not to women at high risk for developing ovarian cancer, such as those with a genetic mutation.

Currently, there is no one reliable method for early detection of ovarian cancer among asymptomatic women. Less than 20% of ovarian cancers are found in the early stages before they have spread outside the ovary. One reason they go undetected is that the symptoms of ovarian cancer are fairly non-specific. In the meantime, regular physicals, pelvic exams, and an awareness of family history and other risk factors are important. (For more about ovarian cancer, see the "What is being tested?" section or the article on Ovarian Cancer.)

When is it ordered?

The CA-125 test may be ordered before a woman starts Ovarian Cancer treatment as a baseline to compare against future measurements. During therapy, a healthcare practitioner may order CA-125 testing at intervals to monitor response to therapy. CA-125 may also be measured periodically after therapy is completed.

In some cases, a healthcare practitioner may order a CA-125 test when a woman has a pelvic mass in order to help determine the cause.

Some healthcare providers may order a CA-125 test and a transvaginal ultrasound at regular intervals when a woman is at high risk of developing ovarian cancer.

What does the test result mean?

If CA-125 levels fall during therapy, this generally indicates that the cancer is responding to treatment. If CA-125 levels rise or stay the same, then the cancer may not be responding to therapy. High CA-125 levels after treatment is complete may indicate that the cancer has come back.

If a woman who has been diagnosed with ovarian cancer has a baseline CA-125 level that is normal, then the test is not likely to be useful to monitor her ovarian cancer. In this case, the ovarian cancer may not be producing CA-125 and is not a good marker of disease progression.

In a woman with a pelvic mass, and in a woman with a high risk for developing ovarian cancer, a significantly elevated CA-125 is a concern but does not necessarily indicate ovarian cancer. This finding would prompt further testing and evaluation.

Is there anything else I should know?

Because CA-125 can be high in many normal or benign conditions, such as pregnancy, menstruation, endometriosis, and pelvic inflammatory disease, it is not useful or recommended as a screening test for the general population.

A new tumor marker, human epididymis protein 4 (HE4), may be ordered along with CA-125 to monitor epithelial cell tumors, the most common type of ovarian cancers. These cancers develop from the cells that cover the outside of the ovaries. The use and full clinical utility of this test has yet to be determined.

What is being tested?

Cancer Antigen 125 (CA-125) is a protein that is present on the surface of most, but not all, ovarian cancer cells. This makes the test useful as a tumor marker in specific circumstances. The CA-125 test measures the amount of CA-125 in the blood.

Significantly elevated concentrations of CA-125 may be present in the blood of a woman who has ovarian cancer. Thus the test may be used to monitor the effectiveness of treatment and/or for recurrence of the cancer. However, not all women with ovarian cancer will have elevated CA-125 so the test may not be useful in all cases.

Ovarian cancer is the fifth most common cause of cancer death in women. According to the American Cancer Society (ACS), the lifetime risk of a woman developing ovarian cancer is about 1 in 75 and the lifetime risk of death is 1 in 100. ACS estimates that about 22,000 new cases are diagnosed each year in the U.S. and about 14,000 women die of it.

Currently, less than 20% of ovarian cancers are found in the early stages before they have spread outside the ovary. The primary reason they go undetected is that the symptoms of ovarian cancer are fairly non-specific.

The need for a reliable method for early detection of ovarian cancer among asymptomatic women continues to drive ongoing research. In the meantime, regular physicals, pelvic exams, and an awareness of family history and symptoms are important.

CA-125 is not recommended as a screening test for asymptomatic women because it is non-specific. Small quantities of CA-125 are produced by normal tissues throughout the body and by some other cancers. Levels in the blood may be moderately elevated with a variety of non-cancerous conditions, including menstruation, pregnancy, and pelvic inflammatory disease.

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in the arm.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

Is any test preparation needed to ensure the quality of the sample?

No test preparation is needed.

  1. Is CA-125 always increased in ovarian cancer?

    No, not all ovarian cancers are associated with increased levels of CA-125. Elevated levels have been found in about 80% of women with ovarian cancer.

  2. Does ovarian cancer run in families?

    Family history is a risk factor for ovarian cancer. If you have close family members who have had ovarian cancer, you are at higher risk than someone who has no family history of the disease. Make sure your healthcare providers know about your family medical history. Women who have inherited a mutation in one of the BRCA genes are at high risk of ovarian cancer. For more details, see the article on BRCA1 and BRCA2.

  3. What are some other risk factors for ovarian cancer?

    In addition to family history, other risk factors include increasing age, obesity, and use of hormone replacement therapy. See the American Cancer Society web site for more on this.