The recent availability of the carcinoembryonic antigen (CEA) assay has stimulated great clinical interest in tumor antigens. Carcinoembryonic antigen is not the only specific or tumor-associated antigen currently identified. There are a number of other tumor antigens which have been isolated, some of which are related to CEA and some of which are totally different. There is, for example, a nonspecific cross-reacting antigen (NCA) which has been discovered in certain preparations which were considered originally to be CEA. Nonspecific cross-reacting antigen is a beta globulin (25% carbohydrate) which cross-reacts with antibodies to CEA and may be the nonspecific background element that causes the CEA titer to be elevated in certain nonmalignant diseases. There is also a membrane-associated, low molecular weight tissular autoantigen (MTA) which has been recently identified. However, this material is not antigenetically related to CEA or NCA
