WASHINGTON--Applying a newly developed mathematical model to an updated version of a familiar tumor marker may increase the chance of finding ovarian cancers at an earlier stage, Robert C. Knapp, MD, said at the American Cancer Society Conference on Gynecological Cancers.
"If we could detect ovarian cancer early in asymptomatic women," said Dr. Knapp, professor emeritus of gynecology, Harvard Medical School, "it would make a significant difference in reducing the horrible mortality from this disease."
Currently, three quarters of ovarian cancers are diagnosed at late stages, when the 5-year survival rate is only 20%. Women whose cancers are found at stage I, however, have a 90% chance of surviving at least 5 years.
Evaluate Changes Over Time
Dr. Knapp said that by evaluating changes in several CA125 radioimmunoassays taken over a period of time, using the updated CA125 II test (Centocor, Malvern, Penn), the new algorithm has improved the assay's positive predictive value (PPV) for the risk of ovarian cancer from approximately 2% to 16%.
The new CA125 II radioimmunoassay utilizes M11, a high-affinity antibody, in combination with the OC125 antibody. Its standard curve is stronger and sharper than the original CA125, enhancing resolution and reducing fluctuations, Dr. Knapp said.
The algorithm looks at the initial level of the CA125 marker, as well as the exponential slope of the line connecting the marker readings. It also takes into account any assay variability that might produce false readings in the short term, said biostatistician Steven Skates, PhD, who developed the algorithm and was lead investigator of the study reported at the meeting.