PHILADELPHIATo be effective, the time interval for ovarian
cancer screening should be no more than a year, a screening trial of
22,000 postmenopausal women suggests. In this study, 67 women were
identified with ovarian cancer. For 28 of these women, ovarian cancer
was detected within 1 year of their last CA 125 blood test.
Overall, the investigators found, based on review of longitudinal CA
125 tests, that ovarian cancer started an average of 1.9 years before
it was found clinically. The results were reported at the annual
meeting of the American Association for Cancer Research (AACR).
A 2-Year Window
This means there is about a 2-year window between the
development of ovarian cancer and its clinical detection, said
Steven J. Skates, PhD, one of the study investigators. Dr. Skates is
assistant professor of biostatistics, Massachusetts General Hospital.
The screening trial was conducted at St. Bartholomews Hospital,
London, between 1986 and 1995, under the direction of Ian Jacobs, MD.
In the study, all volunteers underwent an initial prevalence CA 125
test, Dr. Skates reported. Then they were randomized to a further
three annual screens or a control arm. If CA 125 levels exceeded
30 U/mL, the woman was recalled for a pelvic ultrasound and 3-monthly
CA 125 tests for 1 year. If the ultrasound exam was abnormal, a
gynecologic consult was arranged.
All of the study volunteers underwent a follow-up on cancer status in
December, 1997, through the UK National Cancer Registry, Dr. Skates said.
Screening for ovarian cancer, Dr. Skates said, is
an appealing approach to reducing mortality from this disease because
most cases are currently detected in late-stage disease, resulting in
a very low survival rate. A crucial component of designing trials to
test approaches to screening for ovarian cancer is the interval
between regular tests.
Proposed trials, he observed, have intervals ranging from every year,
to every 1½ years, to once every 3 years.
Estimates on the preclinical duration of disease provide vital
information for this design issue, Dr. Skates said. Now
we have an empirical estimate of the preclinical duration of ovarian
cancer. The fact that it is a short 2 years means that if we are
going to screen for ovarian cancer and detect it at an early stage,
screening every year is a requisiteand screening every 2 years
will miss many of the early stages of ovarian cancers.