Diagnostic significance of tumor markers

Progress in the immunological detection of malignant tumors has been delayed by two major obstacles: (a) the lack of true cancer specificity of the known tumor-marker substances; and (b) the lack of a close relationship between the concentration and/or first appearance of the marker antigens and the malignant disease, especially at its early stage. An additional, important, and complicating factor implicating the specificity of the reactions of the test substances is the existence of immunological cross-reactions. Until recently, only two approaches have been pursued to resolve this difficulty of cross-reactivity, both concerned with the antigen. Now there is a third way, namely, the production of monoclonal antibodies. The poor correlation between the stage of the neoplastic disease and the level of circulating tumor markers, e.g., carcinoembryonic antigen, may be explained on a histological basis, or by inherent differences in the carcinoembryonic antigen molecule of different tumor sources. Few studies are available dealing with these problems.