Cancer Antigen 125 (CA-125) Test

Test Overview

Cancer antigen 125 (CA-125) is a protein found on the surface of many ovarian cancer cells. It also can be found in other cancers and in small amounts in normal tissue. A CA-125 test measures the amount of this protein in the blood.

CA-125 is used as a tumor marker, which means the test can help show if some types of cancer are present. Most often, the CA-125 test is used to check how well treatment for ovarian cancer is working or to see if ovarian cancer has returned.

Why It Is Done

The test for cancer antigen 125 (CA-125) may be used to:

• Check to see if treatment for cancer is working. If the level of CA-125 is going down, it usually means that the treatment is working.
• Follow up on a lump or mass found in the pelvic area.
• Check to see if ovarian cancer has returned.
• Check to see if the ovary is the main site of cancer. If a doctor has found a cancer that has spread to another part of the body (metastatic cancer), the doctor may do a CA-125 test to find out where the cancer started. High levels of CA-125 are a strong sign that the cancer started in the ovary. But other types of cancer can increase CA-125 levels too.

Experts do not recommend using the CA-125 test as a screening test for ovarian cancer because it often has false-positive results that can lead to unneeded surgery. But some doctors may recommend the CA-125 test and a transvaginal ultrasound for those who have a very high risk of ovarian cancer, such as those with BRCA gene changes. For these people, the benefits of screening may outweigh the harms.

How It Feels

When a blood sample is taken, you may feel nothing at all from the needle. Or you might feel a quick sting or pinch.

Risks

There is very little chance of having a problem from this test. When a blood sample is taken, a small bruise may form at the site.

Results

Normal

Each lab has a different range for what's normal. Your lab report should show the range that your lab uses for each test. The normal range is just a guide. Your doctor will also look at your results based on your age, health, and other factors. A value that isn't in the normal range may still be normal for you.

High values

• Conditions other than cancer that can cause high CA-125 values may include:
  • Liver disease (such as hepatitis or cirrhosis).
  • Pancreatitis.
  • The first trimester of pregnancy.
• Types of cancer that can cause high CA-125 values include:
  • Ovarian cancer or cancer of the fallopian tubes or endometrium.
  • Cancer of the pancreas, liver, breast, colon, or lung.
  • Cancers that have spread to the lining of the abdomen (peritoneum).