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Questions and Answers About the CA-125 Test

Author: Taylor Tang
What is CA-125?
What is a CA-125 test?
What is the difference between 1st and 2nd generation CA-125 tests?
What is serial CA-125 testing?
How accurate is a CA-125 test for ovarian cancer?
What are all the different possible test results?
What does it mean to have elevated CA-125 levels?
What does it mean if CA-125 levels are not elevated?
Are there any other blood screening tests for ovarian cancer?
Can the CA-125 test monitor the status of ovarian cancer?

What is CA-125?

    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.

What is a CA-125 test?

    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.

What is the difference between first and second generation CA-125 tests?

    The second 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.

What is serial CA-125 testing?

    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.

    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.

    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.

How accurate is a CA-125 test for ovarian cancer?

    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 tumors, 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.

What are all the different possible test results?

    A CA-125 test result of greater than 35 U/ml is generally accepted as being elevated.

    A true positive result is when the CA-125 test identifies a patient as having ovarian cancer, and they do have ovarian cancer.

    A false positive result is when the CA-125 test identifies a patient as having ovarian cancer, and they do not have ovarian cancer.

    A true negative result is when the CA-125 test identifies a patient as not having ovarian cancer, and they do not have ovarian cancer.

    A false negative result is when the CA-125 test identifies a patient as not having ovarian cancer, and they do have ovarian cancer

    Any result of the CA-125 test should be supplemented with transvaginal sonography, rectovaginal pelvic examination, and serial CA-125 testing.

What does it mean to have elevated CA-125 levels?

    Elevated CA-125 levels can be a false positive, benign tumor, ovarian cancer, or another type of cancer.

    A false positive patient will most likely be identified by a physician as being cancer-free. The possibility that normal ovaries are surgically removed due to a false positive result does exist.

    A study done in 1999 by IJ Jacobs screened about 10,000 postmenopausal women over the age of 45 using the CA-125 test alone. Results of that study showed a false positive rate of about 80%.

    From total positive results; patients between the ages of 20-34 have a 17% chance, and patients older than 34 have a 30% chance of having a benign tumor or pre-cancer conditions.

    Benign tumors, pre-cancer conditions, and stage I cancers will result in pelvic surgery and removal of ovaries. This procedure will almost completely eliminate the risk of ovarian cancer.

    Stage II, III, and IV ovarian cancer patients undergo pelvic surgery and are placed on Taxol and platinum based chemotherapy.

What does it mean if CA-125 levels are not elevated?

    Normal CA-125 levels can be a true negative, or a false negative result. Depending on what risk factors exist for the patient, follow-up tests might need to be conducted.

    All negative CA-125 results are verified using other diagnostic methods. The CA-125 test is more accurate for later stage cancers, making it a poor early detection method.

Are there any other blood screening tests for ovarian cancer?

    Other tumor antigens do exist like OVXI, M-CSF, CA 15-3, and CA 19-9. Only OVXI has shown to have diagnostic potential.

    There is currently a tumor marker test that measures levels of plasma lysophosphatidic acid (LPA) being developed.

    A study using the LPA test showed increased levels from 9 of 10 stage I ovarian cancer patients, and all 24 stage II, III, and IV patients.

    There is also a correlation between BRCA1 and BRCA2 gene mutation and ovarian cancer. Women with BRCA1 or BRCA2 mutations have a 23% chance of having ovarian cancer by age 30, and a 63% chance by age 70.

Can the CA-125 test monitor the status of ovarian cancer?

    Further CA-125 tests for stage II, III, and IV ovarian cancer patients during chemotherapy helps to determine the activity of the cancer, and the status of chemotherapy on the cancer.

    If serial CA-125 testing results double beyond normal parameters of the Skate algorithm, then this suggests progression of the cancer.

References

  1. Cancer Epidemiol Biomarkers Prev 2001 May;10(5):489-93
  2. Int J Gynecol Cancer 1999 Nov;9(6):497-501
  3. NIH Consensus Statement 1994 April 4-5;Volume 12 No. 3
  4. Hogberg T, Kagedal B: Long-term follow-up of ovarian cancer with monthly determinations of serum CA-125. Gynecologic Oncology 46(2): 191-198, 1992.
  5. Rustin GJ, Nelstrop AE, Tuxen MK, et al.: Defining progression of ovarian carcinoma during follow-up according to CA-125: a North Thames Ovary Group study. Annals of Oncology 7(4): 361-364, 1996.
  6. Gershenson, David M., McGuire, William P., Ovarian Cancer: Controversies in Management. Churchill Livingstone Inc., 1998
  7. Rev Clin Esp 1998 Aug;198(8):502-5
  8. Tumor Markers CA-125, Abbott AXSYM Systems. List No. 3B41, 69-4128/R4
  9. Curr Opin Obstet Gynecol. 2000 Feb;12(1):39-42. Review
  10. Lancet. 1999 Apr 10;353(9160):1207-10
  11. Int J Cancer 1988 Nov 15;42(5):677-80

  
     
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