From the Guidelines
CA125 levels are a tumor marker primarily used to monitor ovarian cancer, with normal levels typically below 35 U/mL in the blood, and elevated levels potentially indicating ovarian cancer or non-cancerous conditions. The test is most valuable for tracking treatment response and detecting recurrence in patients with known ovarian cancer rather than as a screening tool for the general population. When monitoring treatment, doctors look for trends in CA125 levels over time rather than focusing on a single measurement. If you have elevated CA125 levels, your doctor will likely recommend additional tests such as ultrasound or CT scans to determine the cause, as the test alone cannot diagnose cancer. Some of the key points to consider when interpreting CA125 levels include:
- Elevated CA125 levels may indicate ovarian cancer, but they can also rise due to non-cancerous conditions like endometriosis, pelvic inflammatory disease, liver disease, pregnancy, menstruation, or other cancers 1.
- The test is not specific for ovarian cancer and may be elevated in non-gynaecological malignancies and benign conditions 1.
- Measuring serum carcinoembryonic antigen (CEA) and carbohydrate antigen 19-9 levels in addition to CA-125 may help distinguish primary mucinous ovarian tumours from a gastrointestinal metastasis 1.
- Regular monitoring of CA125 is typically recommended for women undergoing treatment for ovarian cancer or those at high risk. It's also important to note that the utility of CA125 as a screening tool for ovarian cancer is limited, and it is not recommended for average-risk women 1. Instead, it is primarily used to monitor treatment response and detect recurrence in patients with known ovarian cancer. In terms of specific guidelines, the American Cancer Society recommends against screening for ovarian cancer in average-risk women, citing the lack of evidence that it reduces mortality and the potential for harm from false-positive results 1. Overall, CA125 levels should be interpreted in the context of a patient's individual risk factors and medical history, and should be used in conjunction with other diagnostic tests to determine the cause of elevated levels.
From the Research
CA125 Levels
- CA125 is a serum biomarker used to investigate possible ovarian cancer in symptomatic women presenting to primary care 2.
- The standard CA125 cut-off is ≥35 U/ml, but this value may vary depending on age and other factors 2, 3.
- A CA125 level of 53 U/ml equates to a 3% probability of ovarian cancer overall, but this value changes with age, with a value of 104 U/ml in 40-year-old women and 32 U/ml in 70-year-old women equating to a 3% probability 2.
Diagnostic Performance
- The diagnostic performance of CA125 for ovarian and non-ovarian cancer detection in primary care is unknown, but studies suggest it is a useful test, particularly in women ≥50 years old 2.
- CA125 levels can be elevated in patients with pelvic inflammatory disease, which can limit its use for cancer diagnosis in young women 3.
- The test has a high specificity (93%) but low sensitivity (52%) for diagnosing endometriosis, making it a good rule-in test but not a reliable rule-out test 4.
Cut-Off Values
- Different cut-off values for CA125 have been suggested, including 30 units/ml for endometriosis diagnosis 4 and 589.40 kU/L for distinguishing between clear cell carcinoma and endometrioid carcinoma 5.
- The choice of cut-off value depends on the specific clinical context and the desired balance between sensitivity and specificity 2, 5, 4.
Clinical Applications
- CA125 is widely used as a diagnostic biomarker for ovarian cancer, but its role in screening average-risk asymptomatic women is not recommended by professional societies 6.
- The test can be used to guide individual decisions on the need for further investigation or referral, particularly in women with high CA125 levels and symptoms suggestive of ovarian cancer 2, 6.