Tumor markers oncofetal antigens

With few exceptions, an increase in the activity or mass of an enzyme or isoenzyme is not specific or sensitive enough to be used for identifying the type of cancer or the specific organ involvement. An exception is PSA. PSA has mild protease activity and amino acid sequence homology with serine protease of the kallikrein family.It is expressed by normal, benign, hyperplastic, and cancerous prostate glands and minimally by other tissue. Until the application of PSA as a marker for prostate cancer, tumor enzymes had lost most of their popularity for use as cancer markers. Enzymes were used historically as tumor markers before the discovery of oncofetal antigens and the advent of monoclonal antibodies. The abnormalities of enzymes as a marker for cancer are either the expression of the fetal form of the enzyme (isozyme) or the ectopic production of enzymes. 

The discovery of the oncofetal antigens AFP and CEA in the 1960s revolutionized the modern era of tumor markers. AFP was first found in the sera of mice with liver cancer and later in sera of humans with hepatocellular carcinoma. CEA was discovered in 1965 by Gold and Freeman and was known initially as the Gold antigenOncofetal antigens that have been used as tumor markers, including AFP and CEA, are listed in Table 23-9. 

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