Cancer Antigen 125 (CA 125), Serum
Evaluating patients' response to cancer therapy, especially for ovarian carcinoma
Predicting recurrent ovarian cancer or intraperitoneal tumor
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Cancer antigen 125 (CA 125) is a glycoprotein antigen normally expressed in tissues derived from coelomic epithelia (ovary, fallopian tube, peritoneum, pleura, pericardium, colon, kidney, stomach).
Serum CA 125 is elevated in approximately 80% of women with advanced epithelial ovarian cancer, but assay sensitivity is suboptimal in early disease stages. The average reported sensitivities are 50% for stage I and 90% for stage II or greater.
Elevated serum CA 125 levels have been reported in individuals with a variety of nonovarian malignancies including cervical, liver, pancreatic, lung, colon, stomach, biliary tract, uterine, fallopian tube, breast, and endometrial carcinomas.
Elevated serum CA 125 levels have been reported in individuals with a variety of nonmalignant conditions including: cirrhosis, hepatitis, endometriosis, first trimester pregnancy, ovarian cysts, and pelvic inflammatory disease. Elevated levels during the menstrual cycle also have been reported.
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
In monitoring studies, elevations of cancer antigen 125 (CA 125) >35 U/mL after debulking surgery and chemotherapy indicate that residual disease is likely (>95% accuracy). However, normal levels do not rule-out recurrence.
A persistently rising CA 125 value suggests progressive malignant disease and poor therapeutic response.
Physiologic half-life of CA 125 is approximately 5 days.
In patients with advanced disease who have undergone cytoreductive surgery and are on chemotherapy, a prolonged half-life (>20 days) may be associated with a shortened disease-free survival.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
Not useful as a screening assay for cancer detection in the normal population.
Results cannot be interpreted as absolute evidence of the presence or absence of disease.
Serum markers are not specific for malignancy and values may vary by method. Values obtained with different assay methods cannot be used interchangeably.
Some individuals have antibodies to mouse protein (HAMA), which can cause interference in immunoassays that employ mouse antibodies. In particular, it has been reported that serum specimens from patients who have undergone therapeutic or diagnostic procedures that include infusion of mouse monoclonal antibodies may produce erroneous results in such assays. Rerunning the specimen in question after additional blocking treatment may resolve the issue.
Clinical Reference Provides recommendations for further in-depth reading of a clinical nature
1. Devarbhav H, Kaese D, Williams AW, et al: Cancer antigen 125 in patients with chronic liver disease. Mayo Clin Proc 2002;77:538-541
2. Sturgeon CM, Duffy MJ, Stenman UH, et al: National Academy of Clinical Biochemistry laboratory medicine practice guidelines for use of tumor markers in testicular, prostate colorectal, breast, and ovarian cancers. Clin Chem 2008 Dec;54:11-79
3. Sugiyama T, Nishida T, Komai K, et al: Comparison of CA 125 assays with abdominopelvic computed tomography and transvaginal ultrasound in monitoring of ovarian cancer. Int J Gynaecol Obstet 1996;54:251-256