Current status of carcinoembryonic antigen (CEA) and CEA-S assays in the evaluation of neoplasm of the gastrointestinal tract.

Carcinoembryonic antigen (CEA) is heterogeneous and may represent a set of closely related glycoproteins which have been referred to as isomeric species of CEA. The existence of other CEA-related glycoproteins such as non-specific cross reacting antigen (NCA) has been recognized. Recently a highly purified homogeneous isomeric species of CEA described as CEA-S has shown differences in diagnostic results upon analysis of clinical sera as well as quantitative immunochemical differences. In a blind study of 308 sera, the CEA and CEA-S assays were compared. A significant difference in false positive results was observed between the CEA and CEA-S assay results. In contrast to the low but significant evidence of elevated CEA in sera of random normal persons and patients with liver disease or inflammatory disease of the gastrointestinal tract or lung, none of the sera had elevated concentrations of CEA-S. Among patients with tumor of the gastrointestinal tract that were considered surgically resectable, 46 percent were elevated using the CEA-S assay and only 34.7 percent were elevated above 5 nanograms per ml by the CEA assay. The CEA assays detect CEA-related molecules produced by lung, breast and other tumors; the CEA-S assay appears equally sensitive to CEA of gastrointestinal origin but detects only a small subgroup of breast, lung and, rarely, other types of tumors.