Monoclonal antibodies against carcinoembryonic antigen (CEA) discriminate between CEA produced by gastrointestinal tumors and CEA produced by other tumors

Carcinoembryonic antigen (CEA) is a common tumor marker. It is not specific since many tumor types express it. We report here the use of a series of monoclonal anti-CEA antibodies with apparent restricted activity. These antibodies reacted histochemically with CEA produced by tumors originating in the gastrointestinal tract, but they did not react with CEA-secreting tumors of nongastrointestinal origin. We have used this phenomenon to accurately diagnose the tumor of origin in 20 patients who had a CEA-producing metastatic tumor, but in whom the primary origin was clinically not yet antibodies for diagnostic purposes may be an adjunct to other methods in evaluating tumors of unknown origin.