Medical Health Encyclopedia

CA-125 is a protein that is secreted by ovarian cancer cells and is elevated in over 80% of patients with ovarian cancer. The CA-125 blood test is not approved for screening in the general population. Oncologists will usually only obtain a blood test for this protein if ovarian cancer is strongly suspected or has been diagnosed. In general, a CA-125 level is considered to be normal if it is less than 35 U/mL (microns per milliliter). The test may also be useful for evaluating tumor growth and predicting survival in patients with recurrent cancer who have been treated with topotecan or paclitaxel-carboplatin chemotherapy regimens.

The test is not useful for diagnosis or early screening, however. In approximately half of women with very early ovarian cancer, CA-125 levels are not elevated above the normal standard at all. Furthermore, an elevated level can be caused by a number of other conditions including the following:

• Endometriosis (which may be a risk factor for ovarian cancer).
• Fibroids.
• Noncancerous ovarian cysts.
• Pregnancy.
• Pelvic inflammatory disease.
• Liver diseases.
• Other tumors, such as breast, colon, lung, and pancreatic cancers.
• Age and menstrual status can also affect the levels of CA-125.

Investigative Tests

Ongoing research is underway to find better tests that will detect this cancer in early stages.

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Proteomics. A promising new approach relies on a technique called proteomics. Proteomics is the analysis of certain proteins. In this case, researchers are looking at a unique pattern of proteins produced by ovarian cancer cells. Studies suggest this set of proteins serves as an early biomarker for detecting ovarian cancer. Scientists at the NCI and FDA have developed a blood test to check for the presence of these abnormal proteins. In one study, the proteomics tool identified 100% of patients with ovarian cancer and incorrectly diagnosed cancer in only 3 out of 66 of women who were actually cancer-free. A clinical trial is now underway comparing the proteomics test to the CA-125 test. OvaCheck, another investigational ovarian cancer blood test, is based on principles similar to the NCI/FDA platform, but is being developed independently by a private corporation.