Carbohydrate antigen 125 is a specific oncomarker for ovarian cancer. CA-125 is present in the healthy endothelial tissue of the uterus, but its entry into the bloodstream is minimal due to physiological barriers. However, a significant increase in the level of CA-125 indicates a high probability of ovarian cancer. Oncomarkers often help to identify such a serious disease even at the stage of preclinical manifestations. Due to the balance of price and information quality of the test, CA-125 is considered a screening test to identify a group of individuals at high risk for ovarian cancer from a broader population. In other words, the antigen does not confirm or deny the diagnosis, but it indicates the need for a more detailed examination.

Upon detection of a tumor and its surgical treatment, CA-125 is necessary to monitor the treatment's effectiveness: its concentration must decrease. A subsequent increase indicates a possible recurrence of the disease or the presence of metastases. Upon complete recovery, the level of CA-125 approaches zero.

In addition to oncological reasons for elevated CA-125 levels, there are several other reasons why similar examination results are possible. For example, during menstruation, CA-125 can still enter the blood from the uterine endothelium, leading to an increase in its concentration. False positive results can occur during pregnancy, liver diseases, and endometriosis.