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Antigens that are commonly present both in fetal tissue during early development of life and in adult tissue when cancer occurs. These antigens, primarily glycoprotein in nature, are the products of one or more genes that normally are expressed only during fetal development and then are repressed in adult life. Their production in adults is a result of activation of the controlled genes by a yet unknown mechanism in association with cancer. Minute but significant changes of these fetal antigens in body fluids can serve in detecting the early oncogenic process and in monitoring the efficacy of, and in developing new modalities of, cancer treatment. See Antigen
Several oncofetal antigens have been investigated extensively, including alpha fetoprotein, carcinoembryonic antigen, and prostate specific antigen.
Alpha fetoprotein is a normal embryonic product during fetal development. After birth the serum alpha fetoprotein decreases to only trace amounts by 2–5 weeks, and to normal adult levels (less than 20 nanograms per milliliter) within 1 year. Alpha fetoprotein in the serum is elevated in individuals with primary hepatocellular carcinoma and with teratocarcinomas of the ovary or testes. Nonhepatic primary cancer generally exhibits an elevation of serum alpha fetoprotein only after spread to the liver.
The carcinoembryonic antigen of human digestive cancer has been the most studied oncofetal antigen. Although it is generally accepted that the carcinoembryonic antigen assay should not be used as a screening test for cancer in the general population, it does have an adjunctive role in diagnostic procedures. One of the more significant results in clinical applications of carcinoembryonic antigen is the use of radioactive-labeled antibodies for localization of carcinoembryonic antigen–producing tumors. Although carcinoembryonic antigen is not specific for malignant disease, it is found in association with a variety of epithelially derived cancers.
Prostate specific antigen is expressed exclusively by human prostate epithelial cells. An elevated level of this antigen in the blood is detected in individuals with prostate cancer, although a slightly elevated antigen also can be detected in individuals with benign prostatic hypertrophy, that is, older men with an enlarged prostate. Prostate specific antigen is the most effective parameter for monitoring the treatment response and detecting the early disease recurrence in individuals with an established diagnosis of prostate cancer. Moreover, prostate specific antigen is of clinical value as a reliable aid in the screening of the high-risk or older population for early detection of prostate cancer.