CA-125 is a protein that is found in higher amounts in ovarian cancer cells than in other kinds of cells. This protein enters the bloodstream and can be measured with a CA-125 test, which consists of taking a blood sample from a vein and then measuring the level of CA-125 in the sample.

The test is usually used to evaluate ovarian cancer treatment for a woman who has already been diagnosed or to check on a woman whose cancer is in remission. Normal CA-125 values vary depending on the lab running the test. In general, levels below 35 units per milliliter are considered normal. In a woman who has been diagnosed with ovarian cancer, a decrease in CA-125 usually means the disease is responding to treatment. An increase in CA-125 typically indicates that the disease has gotten worse or has come back.

The CA-125 test is not an effective method of screening healthy women for ovarian cancer because the test has a high false positive rate—in other words, an elevated CA-125 level usually does not indicate ovarian cancer. But it can point to many problems, such as other types of cancer and many other conditions, including uterine fibroids, endometriosis, benign ovarian cysts, pelvic inflammatory disease, cirrhosis of the liver, and a first-trimester pregnancy.

If a healthy woman has an abnormal CA-125 test result, she will need further tests to confirm it and make a specific diagnosis. These tests could include surgical procedures that involve additional risks. Studies are being conducted to determine whether the CA-125 test can be effective for early diagnosis of ovarian cancer in healthy women if used in combination with other blood tests and sonograms. When the cancer is detected at its earliest stage and has not spread from the ovaries, more than 90 percent of women will live at least 5 years.

ADDITIONAL FACTS

  1. Only 1 in 3,000 women has ovarian cancer. However, 21,000 new cases of ovarian cancer are diagnosed in the United States annually.
  2. Only 20 percent of ovarian cancer cases are detected early. When ovarian cancer is first detected at a later stage, after it has spread, only about 30 percent of women with this cancer will survive 5 years.
  3. In the United States, 15,000 women die of the disease each year.