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withdrawn from her markedly swollen belly (sort of like a Pap smear).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. 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 best way to identify ovarian cancer is 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.
Click here for related information.
Created: 2/27/2001 - Donnica Moore, M.D.
