SERUM TUMOR MARKERS

With the advent of new generations of chemotherapeutic agents andadvances in radiation therapy in the management of malignancies, an understanding of tumor markers is becomingincreasingly important. These soluble molecules in the blood are usually glycoproteins detected by monoclonalantibodies. Each tumor marker has a variable profile of usefulness for screening, determining diagnosis and prognosis,assessing response to therapy, and monitoring for cancer recurrence. Monoclonal antibodies are used to detect serumantigens associated with specific malignancies. These tumor markers are most useful for monitoring response totherapy and detecting early relapse. With the exception of Prostate-Specific Antigen (PSA), tumor markers do not havesufficient sensitivity or specificity for use in screening. Cancer Antigen (CA) 27.29 most frequently is used to followresponse to therapy in patients with metastatic breast cancer. Carcinoembryonic antigen is used to detect relapse ofcolorectal cancer, and CA 19-9 may be helpful in establishing the nature of pancreatic masses. CA 125 is useful forevaluating pelvic masses in postmenopausal women, monitoring response to therapy in women with ovarian cancer,and detecting recurrence of this malignancy. Alpha-fetoprotein (AFP), a marker for hepatocellular carcinoma,sometimes is used to screen highly selected populations and to assess hepatic masses in patients at particular riskfor developing hepatic malignancy. Testing for the beta subunit of human chorionic gonadotropin (b-hCG) is an integralpart of the diagnosis and management of gestational trophoblastic disease. Combined AFP and b-hCG testing is anessential adjunct in the evaluation and treatment of nonseminomatous germ cell tumors, and in monitoring theresponse to therapy. AFP and b-hCG also may be useful in evaluating potential origins of poorly differentiatedmetastatic cancer. PSA is used to screen for prostate cancer, detect recurrence of the malignancy, and evaluatespecific syndromes of adenocarcinoma of unknown primary. This review article describes the use of common tumormarkers in primary care practice. Particular emphasis is given to when these tests should be ordered and to commonfactors that influence the interpretation of tumor marker levels.