Should Women Demand CA-125 Screening for Ovarian Cancer?

By Susan Dudley, PhD

Should women demand CA-125 screening for ovarian cancer? No.

A widely circulated email message urges women to demand that their doctors test them regularly for early signs of ovarian cancer. It tells the story of a nurse named Kathy, whose cancer was diagnosed at an advanced stage. It claims that a simple blood test for "CA-125" could have found Kathy's cancer earlier and improved her chances for survival.

Most people would agree that finding cancer early is an important goal. Unfortunately, however, there is no screening test - not even the CA-125 test - that can detect ovarian cancer in the way that mammograms detect breast cancer or Pap smears detect cervical cancer.

Facts about ovarian cancer

Of all the cancers that strike only women, ovarian cancer is the deadliest. About 16,000 women die from the disease each year.

About 22,000 new cases of ovarian cancer are diagnosed each year. Only about 1 in 4 is found at an early stage - before it has spread to other organs of the body. About 90% of women with early-stage diagnoses survive longer than five years, but only 25% of the women diagnosed with advanced ovarian cancer will live that long.

Ovarian cancer has been called a "silent" disease, because it was believed that there are no symptoms until it is very advanced. The fact that women do experience early symptoms is now more commonly recognized. Still, it is difficult to diagnose ovarian cancer because the symptoms often mimic other, more common diseases. They can include: abdominal pressure, bloating or discomfort; frequent or persistent nausea, indigestion or gas; urinary frequency, constipation or diarrhea; abnormal bleeding; unusual fatigue or shortness of breath; or unexplained weight gain or loss.

What is CA-125?

Cancer antigen 125 (CA-125) is a sugar protein that may be released into the bloodstream when various body parts, including the ovaries, are inflamed or injured. It is true that levels of CA-125 can be elevated by ovarian cancer, but this is not always the case - about 20% of women with the disease continue to have normal CA-125 levels. In addition, in spite of its name, CA-125 can also be increased as a result of conditions that have no connection to cancer, such as early pregnancy, endometriosis, or even a common cold.

Because it can come from so many unrelated sources, testing for CA-125 levels simply will not provide your doctor with enough information to diagnose or to rule out ovarian cancer. If all women got this test routinely - as the email suggests they should - then there would be many thousands of false positive as well as false negative results reported each year. In the end, women would not be any better off in terms of more accurate or earlier detection of ovarian cancer, and far too many would be subjected to major abdominal surgery that isn't, in fact, needed.

There are two exceptions where routine CA-125 testing might be useful. First is for women who have already survived ovarian cancer and need to be checked regularly for possible recurrence. The second is women whose mother, daughter, or sister has had the disease, because they may be at higher risk too. In such cases, an elevation of CA-125 might have a higher probability of being associated with ovarian cancer than among women in the general population. Once women tell their health care providers about a personal or family history of ovarian cancer, a regular CA-125 test might be performed - although it still cannot be used alone to determine whether or not ovarian cancer is present, and other types of monitoring would still be needed.

Conclusion: The CA-125 test can't be used to screen for ovarian cancer

Because ovarian cancer is the fifth leading cause of cancer death among women in the United States, there is no doubt that a simple and reliable screening test is needed. In fact, extensive research to develop one has been underway for several years. Some media reports have even suggested - prematurely - that a new test is just around the corner. At the present time, however, no such test exists, and the CA-125 test is not an appropriate solution to this problem.