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The Role of CA125 for Ovarian Cancer

Ovarian cancer is the second most common gynecologic cancer in the United States. Unfortunately, it also causes more deaths than any other female reproductive system cancer. This includes cervical and uterine cancers.1

The American Cancer Society estimates that more than 21,000 women* will be diagnosed with ovarian cancer in 2021. It is also estimated that more than 13,000 will die from ovarian cancer.1

Not everyone shows symptoms of cancer early in the disease. Some cancers are also harder than others to find. This makes screening tests very helpful.

Screening tests are used for people who do not have symptoms but are at risk of developing a disease. Screening tests do not diagnose illness. However, these tests can give your doctor an idea if they should do more testing. Screening tests can be images like X-rays or mammograms. They can also be blood tests or biopsies.

What is CA-125?

CA-125 is a biomarker short for "cancer antigen 125." Biomarkers are often proteins that the body creates. Biomarkers are associated with certain diseases. CA-125 is a protein made on the surface of specific cells and is often found in those with ovarian cancer.2

High levels of CA-125 are found in more than 80 percent of women with late-stage ovarian cancer. High levels are also found in 50 percent of women living with early-stage ovarian cancer. Some of this protein will float around in the blood and can be found using a blood test.2

When will my doctor test for CA-125?

A CA-125 test is often ordered when a doctor is worried that a woman might have ovarian cancer. However, a positive CA-125 test is not enough to diagnose ovarian cancer.2

If you have a positive CA-125 test, your doctor will also order imaging like an ultrasound and a CT scan of your abdomen and pelvis. They also may schedule a biopsy. This is because CA-125 can also be increased in other disorders. It also may not be high at all. Other conditions where levels of CA-125 may be high include diverticulitis, endometriosis, cirrhosis of the liver, pregnancy, and uterine fibroids.2

Because CA-125 is not always predictable, it is not a good screening test for women who are not at risk of ovarian cancer. It is not a routine test like pap smears or mammograms. Your doctor orders this test if there is a strong suspicion of ovarian cancer or if you have certain risk factors. These risk factors include:3

  • Genetic risk factors like having the BRCA 1 or 2 gene
  • Family members who have or had ovarian cancer
  • A history of uterus, breast, or colon cancer

Should we check CA-125 levels anyway?

You might be asking if it is worth it to check CA-125 levels anyway. However, studies disagree. They found that screening every woman, regardless of their risk, was not helpful. It did not improve their likelihood of surviving ovarian cancer if CA-125 was found in their blood. In fact, it put women at greater risk of unnecessary procedures.2

Are there other times where a CA-125 level is useful?

If you are diagnosed with ovarian cancer, your CA-125 level can be used as a baseline. Studies found that regardless of the level, it will decrease if treatment is effective. Because of this, your doctor may order this test multiple times. They can track your CA-125 level over time to see if your treatment is working.2

What does this mean for me?

Ovarian cancer screening starts with family history. Doctors routinely ask about what diseases other family members have. This information is important to help them know your risk for disease. Your doctor will also ask you about any symptoms you may be having.4

If you are concerned about your risk for ovarian cancer or want more information on the CA-125 test, talk to your doctor.

*Note: In this article, the word "women" is used often. However, we recognize that not all people who identify as women have ovaries, and not all people with ovaries identify as women.

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