SERUM TUMOR MARKERS

Abstract

With the advent of new generations of chemotherapeutic agents and
advances in radiation therapy in the management of malignancies, an understanding of tumor markers is becoming
increasingly important. These soluble molecules in the blood are usually glycoproteins detected by monoclonal
antibodies. 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 serum
antigens associated with specific malignancies. These tumor markers are most useful for monitoring response to
therapy and detecting early relapse. With the exception of Prostate-Specific Antigen (PSA), tumor markers do not have
sufficient sensitivity or specificity for use in screening. Cancer Antigen (CA) 27.29 most frequently is used to follow
response to therapy in patients with metastatic breast cancer. Carcinoembryonic antigen is used to detect relapse of
colorectal cancer, and CA 19-9 may be helpful in establishing the nature of pancreatic masses. CA 125 is useful for
evaluating 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 risk
for developing hepatic malignancy. Testing for the beta subunit of human chorionic gonadotropin (b-hCG) is an integral
part of the diagnosis and management of gestational trophoblastic disease. Combined AFP and b-hCG testing is an
essential adjunct in the evaluation and treatment of nonseminomatous germ cell tumors, and in monitoring the
response to therapy. AFP and b-hCG also may be useful in evaluating potential origins of poorly differentiated
metastatic cancer. PSA is used to screen for prostate cancer, detect recurrence of the malignancy, and evaluate
specific syndromes of adenocarcinoma of unknown primary. This review article describes the use of common tumor
markers in primary care practice. Particular emphasis is given to when these tests should be ordered and to common
factors that influence the interpretation of tumor marker levels.