What is a CA-125 (Cancer Antigen 125) test?

From the Guidelines

A CA-125 (Cancer Antigen 125) test is a blood test used to measure the level of CA-125, a protein that can be found in higher amounts in women with ovarian cancer.

Key Points About CA-125 Test

• The test has limited sensitivity and specificity, meaning that it can produce false-positive and false-negative results 1.
• Only half of early ovarian cancers produce enough CA-125 to cause a positive test, and noncancerous diseases of the ovaries, other cancers, and other noncancerous influences can also increase CA-125 levels 1.
• The test is not recommended for screening average-risk women for ovarian cancer, as it has not been shown to reduce ovarian cancer mortality and can lead to unnecessary surgical interventions 1.
• Women with a known hereditary ovarian cancer syndrome, such as mutations on BRCA1 and BRCA2, may be offered annual CA-125 determinations and transvaginal ultrasound as part of their screening protocol 1.

Use of CA-125 Test in Clinical Practice

• The test may be used in conjunction with other screening methods, such as transvaginal ultrasound, to detect ovarian cancer in high-risk women 1.
• The Risk of Ovarian Cancer Algorithm (ROCA), which uses age and longitudinal changes in CA-125 levels to determine the risk of ovarian cancer, is being studied as a potential screening tool, but its effectiveness has not been proven 1.

From the Research

Definition and Purpose of CA-125 Test

• The CA-125 test measures the level of Cancer Antigen 125, a high molecular weight glycoprotein, in the blood 2, 3.
• CA-125 is expressed by a large proportion of epithelial ovarian cancers, but it can also be elevated in other conditions, including benign diseases and other types of cancer 2, 3.

Clinical Use of CA-125 Test

• The CA-125 test is commonly used to monitor the response to therapy and detect tumor recurrence in ovarian cancer patients 3.
• However, due to its low sensitivity and specificity, CA-125 is not recommended as a screening test for ovarian cancer in the general population 2, 3.
• The test may be used to investigate a wide range of signs and symptoms, but its results should be interpreted with caution due to the high false positive rate 2.

Reference Values and Interpretation

• The classical reference value for CA-125 is 35 U/mL, but some studies suggest that this value may not be valid for all populations 4.
• A proposed reference value for CA-125 in healthy men is 20.17 U/mL, which is significantly lower than the commonly used value 4.
• Elevated CA-125 levels can be seen in various benign conditions, including menstruation, pregnancy, and pelvic inflammatory diseases 3.
• A marked increase in CA-125 levels (>1000 units/mL) may be seen in some benign conditions, limiting the value of CA-125 as a diagnostic marker for malignancy 3.

Diagnostic Accuracy and Clinical Applications

• CA-125 has been shown to be a better marker to differentiate endometrial cancer and abnormal uterine bleeding, with 52.63% sensitivity and 80.00% specificity 5.
• In ovarian cancer diagnosis, women with normal CA-125 levels tend to have indolent tumors and are more commonly diagnosed at an early stage, despite longer intervals between testing and diagnosis 6.
• The odds of being diagnosed with early-stage disease are higher in women with normal CA-125 levels compared to those with abnormal levels 6.