March 10, 2009 -- A blood test to detect elevated levels of the protein CA125 -- combined with ultrasound -- may prove to be an effective screening strategy for ovarian cancer in its earliest and most treatable stages, new research suggests.
Very early findings from the largest randomized ovarian cancer screening study ever conducted are promising, researchers say.
But it will be several years until it is clear if the screening method evaluated in the trial saves lives.
More than 200,000 postmenopausal women in the U.K. are participating in the study, which will end in 2014.
"These early results show that screening is feasible," study researcher Usha Menon, MD, of the University College London tells WebMD. "But we don't yet know if this screening saves lives and if so, at what cost. The hope is that we will have these answers in 2014."
Most Ovarian Cancers Found Late
Ovarian cancer is highly treatable when detected early, with a survival rate of 92% at least five years after being diagnosed. But more than two out of three patients are diagnosed with advanced-stage disease, when the five-year survival rate is only 20% to 30%.
More than 21,000 new cases of ovarian cancer were diagnosed in the U.S. in 2008, and more than 15,000 women died from the disease, according to American Cancer Society.
This is why the stakes are so high for the development of an effective screening strategy to detect ovarian cancer in its earliest stages, Menon says.
The CA125 blood test, first developed in the early 1980s, measures a protein that is elevated in ovarian cancer patients. The second generation of the test has proven useful for evaluating how well patients respond to ovarian cancer treatments.
But its usefulness as a screening tool to detect ovarian cancer is more controversial because false-positive rates tend to be high, leading to unnecessary follow-up testing and surgery.
In the U.K. study, researchers evaluated a new way of using the CA125 blood test, which they hope will prove more useful for diagnosing the disease.
Traditionally, a CA125 level of 35 or above has been considered elevated and a level of CA125 below this has been considered normal.
But in the risk-assessment model developed by Menon and colleagues, a woman's absolute CA125 level is less important than changes in CA125 from year to year. Age is also considered, since ovarian cancer risk increases with age.
CA125 Plus Ultrasound
The ongoing U.K. study includes 202,638 postmenopausal women between the ages of 50 and 74 at recruitment between 2001 and 2005 who were randomly assigned to undergo no screening, annual screening with ultrasound alone, or annual screening with ultrasound and the CA125 blood test for 10 years.
Early results from the trial show that CA125 plus ultrasound detected 90% of the ovarian cancers identified so far in the combined screening group, while ultrasound alone identified 75% of cancers reported in this screening group.
Almost half of the cancers detected in both screening groups were early-stage cancers. The total number of cancers detected in the two screening groups was similar.
But the combined-screening group had fewer repeat tests and almost nine times fewer surgeries performed to confirm disease for every ovarian cancer detected.
Thirty-five surgeries were performed to detect one cancer in the ultrasound alone group compared to three surgeries for every cancer detected in the combined screening group.
The study is published in the April issue of The Lancet Oncology.
American Cancer Society Director of Cancer Screening Robert A. Smith, PhD, says final results from the U.K. trial, along with as yet unpublished results from a study conducted by the National Cancer Institute, should reveal more about whether CA125 and ultrasound will prove useful for routine screening.
"For two decades we have been exploring ways to effectively use CA125 and ultrasound to screen for ovarian cancer," he says. "If these studies conclude that these new methods of using these tools have a favorable benefit-to-harm ratio, routine screening for ovarian cancer may become a reality for postmenopausal women."