CA 15-3 test
The CA 15-3 test measures the levels of a specific glycoprotein known as carbohydrate antigen 15-3, which is primarily associated with breast cancer but can also be elevated in other conditions and cancers, including ovarian, prostatic, and lung cancers. Classified as a member of the mucin family of proteins, CA 15-3 plays a role in cell interaction and tumor dynamics. Though not specific or sensitive enough for screening, it serves as a tumor marker to monitor treatment response and recurrence in breast cancer patients, with elevated levels indicating a larger tumor burden. The test is performed through a simple blood draw, with results interpreted using established reference intervals, generally considering levels above 31 units per milliliter as elevated. No special preparation is required for patients, and the risks associated with the procedure are minimal, primarily related to the venipuncture itself. Additionally, research suggests that CA 15-3 testing may provide prognostic value in asymptomatic early breast cancer cases. Overall, the CA 15-3 test is a less invasive option for ongoing cancer management and monitoring.
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CA 15-3 test
ALSO KNOWN AS: Carbohydrate antigen 15-3, cancer antigen 15-3
DEFINITION: CA 15-3 is a transmembrane glycoprotein (carbohydrate-containing protein) found in several tissue types. It is classified as a MUC1 member of the mucin family of proteins. This class of glycoproteins is thought to play a role in reducing cell-to-cell interaction and inhibition of tumor cell cytolysis. The core protein component is identical; the carbohydrate concentration (degree of glycosylation) is the component differentiating between tissue types. Serum/plasma levels are determined by immunoassay.
Cancers diagnosed: CA 15-3 is not an organ-specific marker and has been found at elevated levels in breast, ovarian, prostatic, and lung cancer. Additionally, increased CA 15-3 levels can be found concomitant with conditions such as breast or ovarian disease, endometriosis, pelvic inflammatory disease, hepatitis, pregnancy, and lactation.
Why performed: Because CA 15-3 is not sensitive or specific enough to be used as a screening test, it is primarily used as a tumor marker for monitoring response to therapy and recurrence in breast cancer patients. At least 80 percent of metastatic breast cancer cases have elevated levels of CA 15-3. Blood levels are typically proportionate to the tumor burden (mass), with higher levels of CA 15-3 indicative of the presence of a larger tumor. This test is also significantly less invasive, harmful, or costly compared with other means of monitoring breast cancer development and treatment. According to a study published in 2023 in the Journal of Breast Cancer, CA 15-3 tests can be particularly useful in asymptomatic, early breast cancer patients in terms of prognostic impact.
Patient preparation: No special patient preparation is required for accurate CA 15-3 analysis.
Steps of the procedure: A blood sample is collected, typically by venipuncture. The collected serum (or plasma) is tested by immunoassay, which involves capturing the CA 15-3 present in the sample by means of monoclonal anti-CA 15-3 antibodies. A second, detection (labeled) antibody is then introduced, which subsequently binds to the CA 15-3/anti-CA 15-3 complex. The addition of a substrate results in a detectable signal, the level of which is directly proportional to the amount of the CA 15-3 present in the sample.
After the procedure: Pressure should be applied to the venipuncture site in order to avoid the development of hematoma (a mass of clotted blood resulting from bleeding under the skin).
Risks: The risks of venipuncture are slight but include excessive bleeding, fainting, hematoma, and infection (always a slight risk any time the skin is broken).
Results: Although each laboratory establishes reference intervals based on the local, normal population, a basic interpretive guideline would place normal at 0–31 units per milliliter (U/mL) and elevated at more than 31 U/mL.
Bibliography
Amer. Cancer Soc. "What Happens after Treatment for Breast Cancer?" Cancer.org. ACS, 31 Jan. 2014. Web. 12 Sept. 2014.
Amer. Soc. of Clinical Oncology. "Topic #4: Follow-Up Tumor Marker Tests and Imaging Tests for People Treated for Breast Cancer." Cancer.Net. ASCO, 2005–14. Web. 12 Sept. 2014.
Amer. Soc. of Clinical Oncology. "Tumor Markers for Breast Cancer." Cancer.Net. ASCO, 2005–14. Web. 12 Sept. 2014.
Berger, Barbara J. Laboratory Tests and Diagnostic Procedures. 6th ed. St. Louis: Elsevier, 2013. Digital file.
Hewala, T. I., et al. "Diagnostic and Prognostic Value of Serum Nitric Oxide, Tumor Necrosis Factor-Alpha, Basic Fibroblast Growth Factor and Copper as Angiogenic Markers in Premenopausal Breast Cancer Patients: A Case-Control Study." British Jour. of Biomedical Science 67.4 (2010): 167–176. PubMed.gov. Web. 12 Sept. 2014.
Pedersen, A. C., et al. "Sensitivity of CA 15-3 and Serum HER2 in the Early Detection of Recurrence of Breast Cancer." Clinical Chemistry and Laboratory Medicine 51.7 (2013): 1511–1519. MEDLINE with Full Text. Web. 12 Sept. 2014.
Ryu, Jai Min, et al. “Prognostic Impact of Elevation of Cancer Antigen 15-3 (CA15-3) in Patients with Early Breast Cancer with Normal Serum CA15-3 Level.” Journal of Breast Cancer 26.2 (2023): 126-135. doi:10.4048/jbc.2023.26.e17. Accessed 18 June 2024.