Early detection of cancer: Immunoassays for plasma tumor markers

Background: Plasma tumor biomarkers are widely used clinically for monitoring response to therapy and detecting cancer recurrence. Only a limited number of them, however, have been used effectively for the early detection of cancer. Objective: To review plasma tumor markers used clinically for the early detection of cancer and to provide expert opinion about future directions. Methods: A literature review, as well as the authors' expert opinion, of plasma tumor markers that have been widely accepted for the early detection of cancer. Results: In the US, only prostate-specific antigen, cancer antigen 125 and α-fetoprotein have been clinically used for the early detection of prostate, ovarian and liver cancers, respectively. Both analytical and clinical issues related to the use of these three markers are discussed. Conclusion: Few plasma tumor markers have been used effectively for the early detection of cancer, mainly because of their limited sensitivity and/or specificity. Multiple approaches have been developed to improve the clinical performance of tumor markers for the early detection of cancer. Metrological traceability and antibody specificity are important issues to ensure comparability of immunoassays for the measurement of plasma tumor markers.