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Cancer antigen 125 (CA125)

Cancer antigen 125 (CA125) is a protein produced by a variety of cells, particularly ovarian cancer cells. It is found in trace amounts in the pleura, pericardium and peritoneum of healthy adults.

Why a CA125 test done

A CA125 test may be done to:

  • check a person’s response to treatment for ovarian cancer
    • This is the main use of CA125 tests.
  • check if ovarian cancer has come back (recurred) after treatment

This test is not currently used as a screening test for ovarian cancer because:

  • CA125 is not higher than normal in many women with early stage ovarian cancer.
  • CA125 may be higher than normal in benign diseases and cancers other than ovarian cancer, so it is not specific to ovarian cancer.

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How a CA125 test is done

A CA125 test is usually done in a private laboratory or hospital laboratory. No special preparation is usually needed.

  • CA125 is usually measured by a blood test.
  • The sample is sent to a laboratory to be analyzed by special machines.

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What the results mean

An increased CA125 value can occur in non-cancerous and cancerous conditions.

  • non-cancerous conditions
    • menstruation
    • pregnancy
    • endometriosis
    • fibroids
    • pelvic inflammatory disease
    • ovarian cysts
    • inflammation of the pancreas (pancreatitis)
    • liver diseases such as cirrhosis or hepatitis
    • inflammation of the tissue surrounding the lungs (pleura)
  • cancerous conditions
    • ovarian cancer
    • uterine cancer
    • cervical cancer
    • breast cancer
    • lung cancer
    • stomach cancer
    • colorectal cancer
    • pancreatic cancer
    • liver cancer

In cancerous conditions:

  • A decrease in, or return to normal values of, CA125 may mean that the cancer has responded well to treatment.
  • An increase in CA125 may mean that the cancer is not responding well to treatment, is still growing or is coming back (recurring).
    • A slight increase may not be significant. The doctor looks at trends in the increase over time.

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What happens if a change or abnormality is found

The doctor will decide if more tests, procedures, follow-up care or additional treatment is needed.

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