CA 125 test
The CA 125 test measures the level of the protein CA 125, a mucinous glycoprotein that can be elevated in certain cancers, particularly ovarian cancer. It serves as a biomarker indicating the presence of cancer, as CA 125 is produced by cancer cells and released into the bloodstream. While commonly associated with ovarian cancer, elevated CA 125 levels can also be observed in other conditions, such as uterine cancer, breast cancer, and lung cancer, as well as benign conditions like endometriosis and ovarian cysts.
The test is performed by drawing blood from a vein, typically in the arm, and requires no special preparation. While an elevated CA 125 level (greater than 35 units per milliliter) can indicate potential cancer, it is not definitive, and the presence of elevated levels does not guarantee a cancer diagnosis. CA 125 testing is particularly useful for monitoring patients with a known cancer diagnosis, though it's important to consider that results may not always align with a patient's clinical progress.
As such, CA 125 levels should be tracked over time in conjunction with other diagnostic methods, such as imaging and surgery, to accurately assess cancer growth and treatment response. Understanding the limitations and proper application of the CA 125 test is essential for both patients and healthcare providers.
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CA 125 test
ALSO KNOWN AS: Cancer antigen 125, CA125, CA-125, CA125-II
DEFINITION: CA 125 is a mucinous glycoprotein that may be elevated in some cancer cells, particularly those associated with ovarian cancer. The CA 125 test measure the level of the protein CA 125, which is produced by cancer cells and circulates in the blood stream.
Cancers diagnosed: Ovarian cancer, uterine cancer, breast cancer, lung cancer
Why performed: CA 125 serves as a biomarker or tumor marker that can indicate the presence of cancer. It is generated on the surface of cells and released into the bloodstream. Concentrations of CA 125 are often elevated in ovarian cancer patients. The test may be used anytime during or after treatment to monitor cancer progress. The test is not, however, a stand-alone diagnosis of cancer since various conditions can cause an increase in CA 125.
Patient preparation: No special preparation is necessary.
Steps of the procedure: To determine the level of CA 125 in a patient, blood is drawn from a vein, typically from the inside of an elbow or sometimes from the back of a hand. The site of extraction is first cleaned with an antiseptic. An elastic band is often applied around the upper arm to apply pressure and cause the vein to engorge with blood. After a needle is inserted into the selected vein, blood is collected in a syringe or an airtight vial. Once the blood is collected, the needle is removed and the puncture site is bandaged to stop any subsequent bleeding.
After the procedure: There may be throbbing or bruising around the extraction site.
Risks: The risks involved in collecting blood to ascertain CA 125 levels include the possibility of excessive bleeding, fainting or light-headedness, blood accumulating under the skin (hematoma), and infection around the puncture site. There is always the possibility of multiple punctures being necessary to find a vein that will yield blood.
Results: A CA 125 level greater than 35 units per milliliter (U/mL) of blood is considered elevated. In many cases, elevated levels are not an indication of cancer but instead can be attributed to other conditions, such as endometriosis and benign ovarian cysts. The lack of specificity is a key problem when using CA 125 as a cancer marker. For example, in one study, 79 percent of women with known ovarian cancers had elevated CA 125, while the other 21 percent showed no elevated CA 125 concentrations.
The CA 125 test is most reliable in patients with a previous cancer diagnosis. However, in a 2024 study published by the Journal of Clinical Oncology, researchers found that CA 125 testing was not always in concordance with a patient's progress, especially in women with platinum-sensitive relapsed ovarian cancer. Therefore, a CA 125 test should not be the sole measure of a patient's progress. Instead, tracking CA 125 levels periodically over time to determine the rate at which levels fluctuate in conjunction with ultrasonic imaging, computed tomography (CT) scans, and surgery is the most efficient way to monitor cancer growth.
Bibliography
Amer. Cancer Soc. "How Is Ovarian Cancer Diagnosed?" Cancer.org. ACS, 11 Aug. 2014. Web. 12 Sept. 2014.
Berger, Barbara J., and Cynthia C. Chernecky. Laboratory Tests and Diagnostic Procedures. 6th ed. St. Louis: Elsevier, 2013. Digital file.
Buys, S. S., et al. "Effect of Screening on Ovarian Cancer Mortality: the Prostate, Lung, Colorectal and Ovarian (PLCO) Cancer Screening Randomized Controlled Trial." JAMA 305.22 (2011): 2295–2303. Print.
Chen, Yi-Bin. "CA-125 Blood Test." MedlinePlus. US NLM/NIH, 30 Oct. 2013. Web. 12 Sept. 2014.
McNulty, Rose. “CA-125 Shows Poor Concordance with Radiologic Progression in Ovarian Cancer.” American Journal of Managed Care, 1 Mar. 2024, www.ajmc.com/view/ca-125-shows-poor-concordance-with-radiologic-progression-in-ovarian-cancer. Accessed 12 June 2024.
Natl. Cancer Inst. "Ovarian Cancer Screening (PDQ)." Cancer.gov. NCI/NIH, 8 Aug. 2013. Web. 12 Sept. 2014.
Reade, C. J., et al. "Risks and Benefits of Screening Asymptomatic Women for Ovarian Cancer: A Systematic Review and Meta-Analysis." Gynecologic Oncology 130.3 (2013): 674–681. Print.
Sikaris, K. A. "CA125—A Test with a Change of Heart." Heart, Lung & Circulation 20.10 (2011): 634–640. MEDLINE with Full Text. Web. 12 Sept. 2014.