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Cancer antigen 15-3 (CA15-3)

Cancer antigen 15-3 (CA15-3) is a protein produced by a variety of cells, particularly breast cancer cells.

Why a CA15-3 test is done

A CA15-3 test may be done to check:

  • a person’s response to treatment for breast cancer
    • This is the main use of CA15-3 tests.
  • if breast cancer has come back (recurred) after treatment

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How a CA 15-3 test is done

A CA15-3 test is usually done in a private laboratory or hospital laboratory. No special preparation is usually needed.

  • CA15-3 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 CA15-3 value can occur in non-cancerous and cancerous conditions.

  • non-cancerous conditions
    • pregnancy
    • lactation
    • endometriosis
    • pelvic inflammatory disease
    • benign breast or ovarian disease
    • liver diseases such as cirrhosis or hepatitis
  • cancerous conditions
    • breast cancer
      • CA15-3 is often increased in advanced breast cancer or when cancer has spread (metastasized).
      • It is rarely increased in women with early stage breast cancer.
    • lung cancer
    • ovarian cancer
    • pancreatic cancer
    • liver cancer
    • stomach cancer

In cancerous conditions:

  • A decrease or return to normal value may mean that the cancer has responded well to treatment.
  • An increase 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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