|Ovarian Cancer Screening Using Ultrasound and CA125 Finds
both Early and Late Stage Cancers, But Also Many False Positives
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
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.
The PLCO is currently scheduled to collect data until 2008.
To view a fact sheet on the PLCO Cancer Screening Trial, please visit http://www.cancer.gov/cancertopics/factsheet/Detection/PLCOOvarianFactSheet.
For more information about cancer, visit the NCI Web site at http://www.cancer.gov or call NCI's Cancer Information Service at 1-800-4 CANCER (1-800-422-6237).
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