Ovarian Cancer Screening Using Ultrasound and CA125 Finds both Early and Late Stage Cancers

A new study from the National Cancer Institute (NCI), part of the National Institutes of Health, shows that currently available screening methods such as transvaginal ultrasound (TVU) and testing for a protein biomarker called CA-125, alone or in combination, can detect ovarian cancer but can also produce many false-positive test results, causing needless surgery. This report, which summarizes preliminary results from the Prostate, Lung, Colorectal and Ovarian (PLCO) Cancer Screening Trial, appears in the November 15, 2005 American Journal of Obstetrics and Gynecology.

These findings, the first published ovarian cancer screening results from NCI's ongoing multicenter PLCO Cancer Screening Trial, are based on an analysis of the trial participants' initial screening tests. CA-125 and TVU have been considered as potential screening techniques, although studies to date have not shown that they can be effective and thus they are not currently recommended. The long-term objective of the PLCO Trial is to determine whether screening with TVU and/or CA-125 decreases ovarian cancer mortality in women age 55 to 74.

Of the 28,816 healthy women who underwent the initial (baseline) screening, 1338 (4.7 percent) had an abnormal TVU and 402 (1.4 percent) had an abnormal CA-125 blood test. Thirty-four women (0.1 percent) had abnormal results in both screening tests. Among the women with abnormal test results, 29 tumors were detected, 20 of which were invasive cancers.

Women who had an abnormal test result in one or both screening tests underwent a variety of diagnostic procedures to determine whether cancer was present, including 570 women who underwent a surgical procedure as follow-up. Thus, 541 women underwent surgery but did not have cancer.

"Ovarian cancer is a disease that is often fatal, and both patients and physicians are anxious to find ways to detect it at an earlier, more curable stage," said first author on the study, Saundra Buys, M.D., University of Utah, Salt Lake City. "However, the results from the initial year of screening show that TVU and CA-125 cannot currently be recommended for widespread use in the general population. Future results from the additional PLCO screenings and subsequent follow-up will be needed before a final assessment of this screening strategy can be made."

Enrollment in the PLCO study began in 1993 and ended in 2001. When they initially enrolled in the study, women in the intervention arm underwent baseline ovarian cancer screening with CA-125 and TVU and received additional annual screenings and follow-up. Women in the control arm of the study were not screened but were observed over time.

The results published in this report reflect analysis of the initial baseline screenings for women enrolled between 1993 and 2001. The results of subsequent years screening with TVU and CA-125 are not yet available, and it is these additional results that will ultimately determine whether this screening strategy is effective in reducing mortality from ovarian cancer. These results will not be available for several years.

At the time of the baseline examination, both TVU and CA-125 had low predictive values, a measure of how likely a person with a positive test result is to have the disease of interest, when used to screen healthy women for ovarian cancer. Many investigators feel that an acceptable predictive value for an ovarian cancer screening test is around 10 percent. The predictive values of these screening tests were 3.7 percent for an abnormal CA-125 test, 1 percent for an abnormal TVU, and 23.5 percent if both tests were abnormal. Although having an abnormality in both tests had a fairly high predictive value, only 9 of the 29 tumors (31 percent) were associated with abnormalities in both tests.

Patricia Hartge, Sc.D., a NCI investigator on the PLCO project, added, "As women are followed for a longer period of time, it will be possible to examine how screening tests behave in special groups of women; for example, those with breast or ovarian cancer in their family." Investigators will also be able to study whether other biological markers which are proposed but unconfirmed are useful for early detection of ovarian cancer.