Ovarian cancer is not common but can be deadly because it is hard to detect early when symptoms may be absent or vague. The goal of screening is to find tumours accurately when they are at a treatable stage.
In Monday's issue of the journal Cancer, researchers in the U.S. report on 4,051 post- menopausal women who had an initial blood test for CA125, a protein that is high in many, but not all, women with ovarian cancer and could also be elevated from harmless cysts. The women were placed in three categories based on the findings.
Over 11 years, 83 per cent of the women remained in the normal-risk category and had the blood test annually.
About 14 per cent were in the intermediate group and had to repeat the test in three months.
Almost 3 per cent were considered to be at high risk and were referred for transvaginal ultasound as a second step of the screening and a consultation with a gynecologic oncologist.
All four women in the study with invasive ovarian cancer were part of the study for at least three years with low-risk scores on the blood test before their CA125 levels rose.
"Given the relatively low prevalence of ovarian cancer in the general population, a screening strategy that minimizes unnecessary operations due to false positive values in crucial," Dr. Karen Lu of the University of Texas MD Anderson Cancer Center in Houston and her co-authors concluded.
The generally accepted limit for balancing risk with benefit would be detecting 10 per cent of invasive ovarian cancers among those who had surgery. In this study, that "positive predictive value" was 40 per cent.
The researchers said the two-step strategy for ovarian cancer screening in postmenopausal women was excellent at identifying patients without ovarian cancer who did not undergo surgery.
"It is not practice-changing at this time," Lu's team said.
The researchers said they are waiting for the results of a randomized study currently being conducted in the U.K. with the same risk algorithm on 200,000 women to address whether deaths from ovarian cancer decrease with the screening.
Other biomarkers for ovarian cancer are also being studied.
The study was funded by MD Anderson, the U.S. National Foundation fro Cancer Research, Golfers Against Cancer, the Tracey Jo Wilson Foundaiton, the Mossy Foundation, the Norton family and Stuart and Gaye Lynn Zarrow.
Several study authors have consulted for diagnostic testing companies.