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Cancer antigen CA-125 in the blood
Medical expert of the article
Last reviewed: 06.07.2025
CA-125 is a glycoprotein present in serous membranes and tissues. In women of childbearing age, the main source of CA-125 is the endometrium, which is associated with cyclic changes in the level of CA-125 in the blood depending on the phase of the menstrual cycle. During menstruation, the concentration of CA-125 in the blood increases. During pregnancy, CA-125 is detected in the placental extract, in the serum of the pregnant woman (first trimester), in the amniotic fluid (16-20 weeks). In healthy women, the level of CA-125 in the blood is affected by the synthesis of this marker in the mesothelium of the abdominal and pleural cavities, pericardium, epithelium of the bronchi, fallopian tubes, ovaries, and in men (in addition to the serous cavities) - in the epithelium of the testes.
Reference values (norm) of CA-125 in women in serum up to 35 IU/ml; during pregnancy - up to 100 IU/ml; in men - up to 10 IU/ml. Half-life is 4 days.
[ Indications for the analysis
Determination of the CA-125 content in serum is used:
- for the diagnosis of recurrent ovarian cancer;
- to monitor treatment and control the progression of ovarian cancer;
- for diagnostics of neoplasms of the peritoneum and pleura;
- for the diagnosis of serous effusion in the cavity (peritonitis, pleurisy);
- for the diagnosis of endometriosis.
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Causes of increased CA-125 in the blood
The concentration of CA-125 in the blood increases in various non-neoplastic diseases involving serous membranes - peritonitis, pericarditis, pleurisy of various etiologies. A more significant increase in the level of CA-125 in the blood is sometimes observed in various benign gynecological tumors (ovarian cysts), as well as in inflammatory processes involving the appendages and benign endometrial hyperplasia. However, in most such cases, the concentration of CA-125 in the blood serum does not exceed 100 IU/ml. A slight increase in the level of this marker is detected in the first trimester of pregnancy, in various autoimmune diseases (collagenoses), hepatitis, chronic pancreatitis and liver cirrhosis.
In patients with congestive heart failure, the concentration of CA-125 in the blood correlates with the level of natriuretic peptides, and therefore can be used as an additional criterion for assessing the severity of heart failure.
The CA-125 blood test is used mainly to monitor serous ovarian cancer and diagnose its recurrences. At a cutoff point of 65 IU/ml, CA-125 has a sensitivity of up to 87%, depending on the stage and histological type of the tumor. In 83% of patients with ovarian cancer, its level is on average 124-164 IU/ml. For serous ovarian cancer, the level of increase in CA-125 in the blood serum depends on the tumor stage: at stages I-II, CA-125 increases in approximately 50% of cases, and at stages III-IV - in all patients. In patients with ascitic forms of ovarian cancer, the concentration of CA-125 in the blood serum can exceed values of 10,000-20,000 IU/ml. Tumor regression with effective chemotherapy or chemoradiation treatment or its removal by surgery is accompanied by a decrease in the content of CA-125 in the blood. An increase in the level of CA-125 in the blood is associated with the progression of the tumor process. To assess the effectiveness of chemotherapy, it is necessary to examine the level of CA-125 in the blood before the start of each course of treatment, and after its completion at intervals of 1-2 months.
Unlike serous ovarian cancer, in other histological types of ovarian cancer (mucinous, endometrioid and clear cell), its content increases in 25-30% of cases. In teratomas and dysgerminomas of the ovaries, an increased level of CA-125 in the blood is recorded only in individual patients with ascites and metastases in the abdominal cavity.
CA-125 is a useful marker for assessing the effectiveness of treatment and early detection of relapses of endometriosis, which ranks second after ovarian cancer in the number of patients with elevated CA-125 levels. An increase in the level of CA-125 in the blood correlates with the stage of endometriosis: at stages I-II, the marker concentration is elevated in 25% of patients, and at stages III-IV - in 54%. As a rule, the concentration of CA-125 in the blood serum of such patients does not exceed 65 IU/ml.
The level of CA-125 increases in 15-30% of patients with malignant tumors of the gastrointestinal tract, pancreas, bronchi, and mammary gland. The values of CA-125 in the blood serum of these patients, exceeding 150-200 IU/ml, indicate the involvement of serous membranes in the process.