Evaluation of a radioimmunoassay for carcinoembryonic antigen of the human digestive system

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Few topics in cancer immunology have given rise to more controversies in the past few years than the detection of circulating tumor antigens. Gold et al made a significant contribution in this regard by demonstrating, isolating, and characterizing what appeared to be both a system- and tumor-specific neoantigen.1–4 Apparently this antigen could be found in all entodermally derived adenocarcinomata of the gastrointestinal tract as well as in fetal gut in the first two trimesters of gestation, hence the name carcinoembryonic antigen (CEA). Using a radioimmunoassay technique,5 they later demonstrated in a study of 200 cases, that circulating levels of this antigen as low as 2.5 ng/ml could be reproducibly detected. The antigen was present in the serum of 35 of 36 patients with adenocarcinoma of the colon and rectum, and disappeared from circulation following complete resection of the tumor mass. Moreover, this antigen could not be detected in the serum of normal individuals or patients with either benign or malignant disease in other systems.

Because of the diagnostic and prognostic significance of these findings we initially undertook the evaluation of Doctor Gold's assay using principal reagents he supplied without modifying his methodology. As is often the case with any new procedure, there were many techical problems, as a result of which only 60% of our initial samples (239 cases) were suitable for study.6 In brief, the sensitivity of the assay was such that only 65% of adenocarcinomata of the colon and rectum and 60% of adenocarcinomata elsewhere in . . .



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