CA 15-3
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- Also Known As:
- CA-Breast
- Cancer Antigen-Breast
- Formal Name:
- Cancer Antigen 15-3

This page was fact checked by our expert Medical Review Board for accuracy and objectivity. Read more about our editorial policy and review process.
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At a Glance
Why Get Tested?
To monitor the response to treatment of invasive breast cancer and to help watch for recurrence of the disease
When To Get Tested?
When you have been or are being treated for invasive breast cancer
Sample Required?
A blood sample drawn from a vein in your arm
Test Preparation Needed?
None
You may be able to find your test results on your laboratory’s website or patient portal. However, you are currently at Testing.com. You may have been directed here by your lab’s website in order to provide you with background information about the test(s) you had performed. You will need to return to your lab’s website or portal, or contact your healthcare practitioner in order to obtain your test results.
Testing.com is an award-winning patient education website offering information on laboratory tests. The content on the site, which has been reviewed by laboratory scientists and other medical professionals, provides general explanations of what results might mean for each test listed on the site, such as what a high or low value might suggest to your healthcare practitioner about your health or medical condition.
The reference ranges for your tests can be found on your laboratory report. They are typically found to the right of your results.
If you do not have your lab report, consult your healthcare provider or the laboratory that performed the test(s) to obtain the reference range.
Laboratory test results are not meaningful by themselves. Their meaning comes from comparison to reference ranges. Reference ranges are the values expected for a healthy person. They are sometimes called “normal” values. By comparing your test results with reference values, you and your healthcare provider can see if any of your test results fall outside the range of expected values. Values that are outside expected ranges can provide clues to help identify possible conditions or diseases.
While accuracy of laboratory testing has significantly evolved over the past few decades, some lab-to-lab variability can occur due to differences in testing equipment, chemical reagents, and techniques. This is a reason why so few reference ranges are provided on this site. It is important to know that you must use the range supplied by the laboratory that performed your test to evaluate whether your results are “within normal limits.”
For more information, please read the article Reference Ranges and What They Mean.
What is being tested?
Cancer antigen 15-3 (CA 15-3) is a protein that is produced by normal breast cells. In many people with cancerous breast tumors, there is an increased production of CA 15-3 and the related cancer antigen 27.29. CA 15-3 does not cause cancer; rather, it is shed by the tumor cells and enters the blood. This test measures CA 15-3 in the blood.
Since CA 15-3 can be measured in the blood, it is useful as a tumor marker to follow the course of the cancer. CA 15-3 is elevated in fewer than 50% of women with early localized, breast cancer or with a small tumor, but is elevated in about 80% of those with breast cancer that has spread (metastatic). Because not all women with invasive breast cancer will have elevated CA 15-3, the test is not useful in all cases.
CA 15-3 is not recommended as a screening test to detect breast cancer in women because it is non-specific. It may also be elevated in healthy people and in individuals with other cancers such as colon, lung, pancreas, ovarian, or prostate malignancies or certain conditions such as cirrhosis, hepatitis, and benign breast disease.
Common Questions
View Sources
Sources Used in Current Review
Pagana, Kathleen D., Pagana, Timothy J., and Pagana, Theresa N. (© 2015). Mosby’s Diagnostic and Laboratory Test Reference. 12th Edition: Mosby, Inc., Saint Louis, MO. Pp 196.
Penn Medicine Oncolink® (28 April 2016 updated). Patient Guide to Tumor Markers. Available online at http://www.oncolink.org/treatment/article.cfm?id=296. Accessed February 2017.
National Cancer Institute (4 November 2015 reviewed). Tumor Markers. Available online at http://www.cancer.gov/about-cancer/diagnosis-staging/diagnosis/tumor-markers-fact-sheet. Accessed February 2017.
Thaker NG (5 September 2014 updated). CA 15-3. Medscape Reference. Available online at http://emedicine.medscape.com/article/2087491-overview. Accessed February 2017.
Graham LJ, Shupe MP, Schneble ED, et al. Current Approaches and Challenges in Monitoring Treatment Responses in Breast Cancer. Journal of Cancer. 2014; 5(1): 58-68. Published online 2014 Jan 5. doi: 10.7150/jca.7047
Molina R, Barak V, Duffy MJ, et al. Tumor Markers in Breast Cancer – European Group on Tumor Markers Recommendations. Available online at http://www.egtm.eu/professionals/breast_cancer. Accessed February 2017.
Chourin S, Georgescu D, Gray C, et al. Value of CA 15-3 Determination in the Initial Management of Breast Cancer Patients. Annals of Oncology. 2009:20(5):962-964. Published online 19 March 2009 doi:10.1093/annonc/mdp061.
Sources Used in Previous Reviews
Thomas, Clayton L., Editor (1997). Taber’s Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition].
Pagana, Kathleen D. & Pagana, Timothy J. (2001). Mosby’s Diagnostic and Laboratory Test Reference 5th Edition: Mosby, Inc., Saint Louis, MO.
Check, W. (1998 July) Reaching agreement on tumor markers. CAP Today, In the News [On-line journal]. Available online at http://www.cap.org/captoday/archive/1998/julycover.html.
NCI (1998 April 27). Tumor markers. National Cancer Institute, Cancer Facts [On-line information]. Available online at http://cis.nci.nih.gov/fact/5_18.htm.
ACS (2000 July 19). Tumor Markers. American Cancer Society, Prevention and Early Detection [On-line information]. Available online through http://www.cancer.org.
AACC (2001 July 27) Use of Tumor Markers in Cancer Patients Leads to Better Detection, Decreasing Mortality. AACC Media Center, American Association for Clinical Chemistry [On-line press release]. PDF available for download at http://www.aacc.org/media/TumorMarkers.pdf.
ASCO (1996 May 17, adopted, revision every 3 years). CA 15-3 as a Marker for Breast Cancer. American Society for Clinical Oncologists, Clinical Practice Guidelines for the Use of Tumor Markers in Breast and Colorectal Cancer [On-line guidelines]. Available online at http://www.asco.org/prof/pp/html/guide/tumor/m_tumor10.htm.
Pagana, K. D. & Pagana, T. J. (© 2007). Mosby’s Diagnostic and Laboratory Test Reference 8th Edition: Mosby, Inc., Saint Louis, MO. Pp 214-215.
Clarke, W. and Dufour, D. R., Editors (© 2006). Contemporary Practice in Clinical Chemistry: AACC Press, Washington, DC. Pp 247.
Wu, A. (© 2006). Tietz Clinical Guide to Laboratory Tests, 4th Edition: Saunders Elsevier, St. Louis, MO. Pp 206-207.
(Revised 2008 December 08). Tumor Markers. American Cancer Society [On-line information]. Available online at http://www.cancer.org/docroot/PED/content/PED_2_3X_Tumor_Markers.asp?sitearea=PED. Accessed August 2009.
(Updated 2009 May) Tumor Markers. ARUP Consult [On-line information]. Available online at http://www.arupconsult.com/resources/print/TumorMarkers.pdf. Accessed August 2009.
Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Burtis CA, Ashwood ER and Bruns DE, eds. 4th ed. St. Louis, Missouri: Elsevier Saunders; 2006, Pp 770-771.
Park, B et al. Preoperative CA 15-3 and CEA serum levels as predictor for breast cancer outcomes. Annals of Oncology 2008 19(4):675-681. Available online at http://annonc.oxfordjournals.org/cgi/content/full/19/4/675. Accessed September 2009.
Merck (2000). Cancer and the Immune System. The Merck Manual of Medical Information Home Edition, Section 15 Cancer, Ch 163 [On-line information]. Available online at http://www.merck.com/pubs/mmanual_home/sec15/163.htm.
Duffy, M. (1999). CA 15-3 and related mucins as circulating markers in breast cancer. Ann Clin Biochem [On-line journal]. Vol 36: 579-586. PDF available for download at http://www.leeds.ac.uk/acb/annals/annals_pdf/Sept%2099/ACB579.PDF.
Srirangam, S. and Harland, R. (2001). Management of Advanced Breast Cancer. Forum for Registrars In Surgical Training [On-line information]. PDF available for download at http://www.frist.org/asit/meetings/yearbook2001/BREAST%20CANCER.pdf.
(Revised 2012 October 18). Tumor Markers. American Cancer Society [On-line information]. PDF available for download at http://www.cancer.org/acs/groups/cid/documents/webcontent/003189-pdf.pdf. Accessed October 2012.
Thaker, N. et. al. (Updated 2012 May 24). CA 15-3. Medscape Reference [On-line information]. Available online at http://emedicine.medscape.com/article/2087491-overview#showall. Accessed October 2012.
(© 1995-2012). Cancer Antigen 15-3 (CA 15-3), Serum. Mayo Clinic Mayo Medical Laboratories [On-line information]. Available online at http://www.mayomedicallaboratories.com/test-catalog/Overview/81607. Accessed October 2012.
Pagana, K. D. & Pagana, T. J. (© 2011). Mosby’s Diagnostic and Laboratory Test Reference 10th Edition: Mosby, Inc., Saint Louis, MO. Pp 206-207.
Clarke, W., Editor (© 2011). Contemporary Practice in Clinical Chemistry 2nd Edition: AACC Press, Washington, DC. Pp 496, 500.
Pagana and Pagana. Mosby’s Manual of Diagnostic and Laboratory Tests. Fourth Edition. Pg 142.
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