New data demonstrates that average-risk women who are screened for ovarian cancer using serum cancer antigen 125 (CA-125) and transvaginal ultrasound do not have a lower ovarian cancer mortality rate than women who receive usual care.

The study, reported at the 2011 American Society of Clinical Oncology (ASCO) meeting, also shows that ovarian cancer screening prompted by a false-positive screening test produces a hike in the complication rate.

Saundra S. Buys, MD, with the University of Utah in Salt Lake City, and associates reported ovarian cancer-specific mortality findings from the Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial. The PLCO study was designed to determine the effect of specific cancer screening tests on cause-specific mortality.

Dr. Buys and her group say that their findings are not due to differences in participant characteristics between the two study arms because they were identical at baseline and also because follow-up was nearly complete in both study groups. In addition, screening was high in the intervention group with little contamination in the usual care cohort.

For the analysis, 78,216 women ranging from 55 to 74 years at 10 U.S. screening centers were randomized to yearly screening or usual care. Individuals who had a history of bilateral oophorectomy were excluded.

According to the study protocol, women assigned to the intervention group were offered annual screening with CA-125 for six years and transvaginal ultrasound for four years. Women in the usual care group were not offered either of the screening tests.

The primary study endpoint was ovarian cancer-specific mortality.

During a maximum 13-year follow-up period, ovarian cancer was diagnosed in 212 women (5.7 per 10, 000 person-years) in the intervention group and 176 (4.7 per 10, 000 person-years) in the usual care group (rate ratio [RR], 1.21; 95% confidence interval [CI], 0.99-1.48). Overall, there were 118 deaths caused by ovarian cancer (3.1 per 10,000 person-years) in the intervention group and 100 deaths (2.6 per 10,000 person-years) in the usual care group (mortality RR, 1.18; 95% CI, 0.82-1.71).

Of 3,285 women with false-positive results, 1,080 underwent surgical follow-up; 163 of them developed at least one serious complication (15%). There were 2924 deaths due to other causes (excluding ovarian, colorectal, and lung cancer) (76.6 per 10,000 person-years) in the intervention group and 2,914 deaths (76.2 per 10,000 person-years) in the usual care group (RR, 1.01; 95% CI, 0.96-1.06).

Dr. Buys and her colleagues believe that although the screening tests as they were employed in this study did not decrease mortality, it is possible that CA-125 and transvaginal ultrasound may provide be benefit if used differently. For example, tracking the changes in CA-125 over time rather than relying on a single CA-125 value may permit earlier detection of cancers at a stage when cure is possible. However, they emphasize that research is needed to support this hypothesis.

In the U.S., ovarian cancer is among the five leading causes of cancer deaths in women. The disease is usually diagnosed at an advanced stage, which is associated with a five-year survival rate of less than 30%.

Written by Jill Stein
Jill Stein is a Paris-based freelance medical writer.