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 discovered. The use of such antibodies for diagnostic purposes may be an adjunct to other methods in evaluating tumors of unknown origin.