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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.
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.
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.
An increased CA125 value can occur in non-cancerous and cancerous conditions.
- non-cancerous conditions
- 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.
The doctor will decide if more tests, procedures, follow-up care or additional treatment is needed.