CA 125: fundamental and clinical aspects

Since the OC 125 monoclonal antibody (Mab) was generated, other Mabs to the CA 125 glycoprotein have been produced and classified into two families associated with two major epitope regions on the CA 125 molecule. New generation assays, combining Mabs to two distinct regions of the molecule, compare favorably with that of the original assays as demonstrated by ROC curves. The original CA 125 assay suffered from interference of HAMA, an important drawback considering the increasing use of murine antibodies for immunodiagnosis and treatment of ovarian cancer. This problem has been solved for the majority of currently available tests. The sensitivity of the assays for early ovarian cancer remains low, precluding its indiscriminate use for screening and diagnosis of ovarian cancer. Its use in screening for early cancer, combined with ultrasonography, is limited to high risk populations, such as women from families with mutations in the BRCA1 or 2 gene. Although CA 125 assessment may play a limited role in the (early) detection of ovarian cancer, its role in the follow-up during and after therapy is well established. The major contribution of CA 125 is in the monitoring of tumor response to chemotherapy, where it is valuable in detecting those patients with an inadequate response to the chosen treatment. The role of CA 125 in early detection of recurrences remains to be established and is currently the subject of two large clinical trials.