Ovarian Cancer Blood Test
Q: I received an email warning about a blood test all women should have to
screen for ovarian cancer. Is this true?
Dr. Donnica: I received the same email message. It presents a compelling story from a woman who was diagnosed with primary peritoneal cancer (closely related to ovarian cancer) after first being repeatedly misdiagnosed, despite having symptoms of ovarian cancer. In her case, the diagnosis was strongly suspected by her symptoms, as well as an analysis of abdominal fluid that was withdrawn from her markedly swollen belly (sort of like a Pap smear). Only then was the CA-125 blood test done, which supported the presumptive diagnosis.
Unfortunately, ovarian cancer is difficult to diagnose early, and it remains the 5th most common cancer killer of women. Ovarian cancer affects one in 57 women. Last year, nearly 22,000 women were diagnosed with ovarian cancer. So why shouldn't every adult woman have this blood test as a screen?
CA-125 is a protein produced by ovarian cancer cells. It is true that CA-125 protein levels in the blood can be measured as a marker for ovarian cancer, but it is not a conclusive test. It is not used for screening because of its poor accuracy; there are some harmless reasons that CA-125 levels can be elevated. In addition, only about half of the women with an early stage ovarian tumor will have an increased level of CA-125 and only 80% of women with an advanced stage ovarian cancer will have an elevated CA-125 level, according to the American Cancer Society.
CA-125 testing is recommended for women at high risk for ovarian cancer, such as those with a family history of ovarian cancer or those who have tested positive for BRCA1 or BRCA-2, the genetic defects for certain breast cancers. The CA-125 blood test is also routinely used for women diagnosed with ovarian cancer to measure their response to treatments, as well as to watch for recurrence. Women who have possible symptoms of ovarian cancer should have a CA-125 blood test along with the rest of their evaluation.
One large published study of 22,000 women (The Lancet, 4/10/99) looked at the effects of screening for ovarian cancer with CA-125. All women were at least 45 years old, postmenopausal, had no history of ovarian cancer, and had not had their ovaries removed. They each had the CA-125 blood test. After the initial baseline screening, half of the women were randomly selected to receive three more annual tests, while the other half received no further tests but were followed by researchers. If a woman's CA-125 levels were elevated, she received pelvic ultrasound examinations, and if abnormalities were detected, she was referred to a gynecologist for a surgical biopsy.
In the group assigned to receive annual screenings, 468 women had elevated CA-125 levels, and 29 were ultimately referred for a surgery. Of those referred for surgery, six were diagnosed with ovarian cancer, while the other 23 had false-positive results -- results that suggested ovarian cancer although the women did not actually have it. Ten more women in the screening group developed ovarian cancer during the eight years they were followed by the researchers. In the control group (the group not receiving annual screening), 20 cases of ovarian cancer were eventually identified.
Women in the screened group lived longer after their ovarian cancer was diagnosed than those diagnosed with ovarian cancer in the control group -- by 31.1 months. This study was not considered large enough, however, to draw conclusions from this information. Currently, two larger studies are underway to confirm the benefit of regular screening for all women. Researchers expect the first results may be available in one to two years.
The study's results confirm the poor accuracy of the screening methods used. The usual screening tests and gynecologic surveillance missed too many existing cancers and blood-screening tests falsely detected too many cancers that did not exist. What's wrong with that? In this study, for each of the six women who were diagnosed with ovarian cancer as a result of regular blood test screening, four additional women underwent unnecessary surgery. An additional 10 women who were screened developed ovarian cancer within eight years although the test did not detect any early evidence of cancer. This poor accuracy of CA-125, even in combination with vaginal ultrasound testing, is the primary reason why the American Cancer Society does not recommend screening with CA-125 for women who are not at high risk.
The good news for women who have had ovarian cancer is that there is now a new blood test available called Architect HE4 which received FDA clearance on June 3, 2010. This protein test is approved to monitor previously diagnosed women for recurrence or progression of ovarian cancer in conjunction with the CA-125 protein assay and other information. Studies have shown that the combined HE4/CA-125 testing, using an algorithm that incorporates test results and patient characteristics, is the most effective available biomarker strategy to predict the presence of cancer in an ovarian mass. This is extremely important because 70% to 90% of women with ovarian cancer who achieve remission suffer from a later recurrence of the disease.
The best way to identify ovarian cancer in the first place remains through an abnormality found on a routine pelvic exam. This means the best preventive measure women can take is to have their annual gynecologic exam. An ultrasound exam can confirm the abnormality. If cancer is suspected, the CA-125 blood test can be ordered as well. This is NOT a reliable screening or diagnostic test for ovarian cancer, however. The only way to make the definite diagnosis is surgically. Depending upon the doctor's level of suspicion, s/he may recommend a laparoscopy, in which a lighted tube is inserted through a small "belly button" incision, or open surgery down the middle of the abdomen, called a laparotomy.
During surgery, the ovaries and all abdominal organs (diaphragm, bowel, and peritoneum) will be carefully examined for any evidence of cancer. Lymph nodes, fluid samples and tissue biopsies will be taken and tested.
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Created: 2/27/2001 - Donnica Moore, M.D.
Reviewed: 6/4/2010 - Donnica Moore, M.D.
