CA-125, cancer antigen-125, is a protein that is found at levels in most ovarian cancer cells that are elevated compared to normal cells. CA-125 is produced on the surface of cells and is released in the blood stream.
The CA-125 test assesses the concentration of CA-125 in the blood. The test requires a sample of the patient's blood to be drawn. The second generation test, compared to the first generation test, is less likely to fluctuate from day to day. The two tests are not interchangeable. The second generation test results are slightly higher than the first generation ones. Both can be used serially as long as the test data in each series is from the same generation test.
Serial CA-125 testing is a series of CA-125 tests repeated over a period of time. Performing several CA-125 test over a period of time allows evaluation of the rate that CA-125 concentration increases. When looking over serial test results check to make sure the test used in each case was the same generation, same manufacturer, and same type of assay.
The rate at which CA-125 levels increase is a more accurate method of detecting the presence of ovarian cancer, than a single CA-125 test. An algorithm by SJ Skates detected 83% of ovarian cancer cases and 99.7% of positive results were truly ovarian cancer. This represents a dramatic improvement on the accuracy of a single CA-125 test.
The CA-125 test only returns a true positive result for about 50% of Stage I ovarian cancer patients. The CA-125 test is not an adequate early detection tool when used alone. The CA-125 test has an 80% chance of returning true positive results from stage II, III, and IV ovarian cancer patients. The other 20% of ovarian cancer patients do not show any increase in CA-125 concentrations.
However several women's reproductive disorders can cause a false positive result. Endometriosis, benign ovarian cysts, first trimester of pregnancy, and pelvic inflammatory disease all produce higher levels of CA-125. 70% of people with cirrhosis, 60% of people with pancreatic cancer, and 20%-25% of people with other malignancies have elevated levels of CA-125.
A study of about 22,000 post menopausal women 45 years or older screened about 11,000 with the CA-125 test. 468 patients with elevated CA-125 levels were given an ultrasonography test. Of those patients, 29 underwent surgical procedures. 6 had ovarian cancers, 2 had adenocarcinoma of unknown origin, 14 had benign cancers, 4 had fibroids, and 3 had no abnormalities. CA-125 test has a lower specificity in premenopausal women than postmenopausal women.
The CA-125 test is not recommended for use alone as an early detection method. The rate of false positives is very high, and there has been no data concerning change in mortality. The CA-125 test should not be used alone to detect ovarian cancer, but rather with transvaginal sonography and rectovaginal pelvic examination for greater accuracy. Combining detection methods lowers the number of false positive results. The CA-125 test should be done serially for best accuracy.