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CA 15.3 Blood Test

Last updated July 23, 2019

Approved by: Maulik P. Purohit MD, MPH

Pan American Health Organization

CA 15-3 Test is a test to detect and measure the amount of CA 15-3 (Cancer Antigen 15-3) in blood. It is used to monitor breast cancer, once it is diagnosed and evaluate the effectiveness of treatment.

What are the other Names for this Test? (Equivalent Terms)

  • CA-Breast Test
  • Cancer Antigen 15-3 Test
  • Cancer Antigen-Breast Test

What is CA 15.3 Blood Test? (Background Information)

  • CA 15-3 Test is a test to detect and measure the amount of CA 15-3 (Cancer Antigen 15-3) in blood
  • CA 15-3 is a protein secreted by breast tissue and found in low levels in normal individuals. The presence of cancerous breast tissue increases the level of CA 15-3
  • CA 15-3 Test is used to monitor breast cancer once it is diagnosed. It is also used to evaluate the effectiveness of treatment. However, this test is not used for screening or diagnosing breast cancer

What are the Clinical Indications for performing the CA 15.3 Blood Test?

  • CA 15-3 Test is ordered after the diagnosis of advanced breast cancer
  • It is ordered either after the surgical removal of breast cancer, or when the patient is receiving treatment for breast cancer. This is done to monitor the recurrence of the tumor or to evaluate the response to treatment
  • Though CA 15-3 test is not recommended for the screening or diagnosis of breast cancer, it is likely to be ordered by a healthcare provider in advanced cases of breast cancer, where either surgery has been performed to remove the tumor or treatment with chemotherapeutic medications have been started
  • The test is generally ordered along with other tests and investigations before the treatment is started, and then ordered periodically to monitor the effect of treatment

How is the Specimen Collected for CA 15.3 Blood Test?

Sample required: Blood

Process: Insertion of needle into a vein (arm).

Preparation required:None

What is the Significance of the CA 15.3 Blood Test Result?

  • Normal reference value of CA 15-3 for both males and females is < 30 U/mL (ā€˜Uā€™ is not defined). Increasing levels of CA 15-3 signify progression of breast cancer. About 80% of individuals with advanced breast cancer will show elevated levels of the protein CA 15-3
  • Increased levels of CA 15-3 correlate with the spread of breast cancer despite treatment, or the return of the cancer after being successfully treated. The greater the size of the tumor or the more the spread of the breast cancer (especially to areas such as liver and bone), the higher will be CA 15-3 levels
  • Elevated levels of CA 15-3 may also be found in some other cases, such as liver disease (hepatitis, cirrhosis), noncancerous breast lesion, and cancers of the lung, colon, pancreas, liver, ovary, cervix, endometrium, and prostate
  • Low levels of CA 15-3 are related to localized type of breast tumor. If the levels start decreasing after initiation of treatment, it usually correlates with the regression of tumor due to effective therapy. Constant levels are associated with a stable disease
  • It is very important to note that normal or low levels of CA 15-3 do not rule out advanced breast cancer, as 20-25% cases of advanced breast cancer will not show CA 15-3 elevation in blood. Likewise 10% of individuals with localized form of breast cancer will show elevated levels of CA 15-3
  • Other lab tests and investigations are also performed along with CA 15-3 to determine the type of tumor and treatment options, once a diagnosis is confirmed

The laboratory test results are NOT to be interpreted as results of a "stand-alone" test. The test results have to be interpreted after correlating with suitable clinical findings and additional supplemental tests/information. Your healthcare providers will explain the meaning of your tests results, based on the overall clinical scenario.

Additional and Relevant Useful Information:

  • CA 15-3 is one of the tumor marker derived from MUC1 gene. A similar type of antigen CA 27.29 is also derived from MUC1 gene. CA 27.29 test can be used as an alternative or combined with CA 15-3 test and other testing, to help the healthcare provider manage treatment for breast cancer
  • However, CA 15-3 is not found to be of much use in predicting future outcomes of advanced breast cancers

Certain medications that you may be currently taking may influence the outcome of the test. Hence, it is important to inform your healthcare provider, the complete list of medications (including any herbal supplements) you are currently taking. This will help the healthcare provider interpret your test results more accurately and avoid unnecessary chances of a misdiagnosis.

References and Information Sources used for the Article:

Reviewed and Approved by a member of the DoveMed Editorial Board
First uploaded: Sept. 4, 2013
Last updated: July 23, 2019