Ideally, the substance produced by the cancer cells would contain identical antigenic markers in every individual where active cells are found. The purified substance would be isolated and well-characterized to permit the development of analytical methods, such as those employing immunoassay principles in which antibodies may be developed specific to epitopes or defined areas of the antigenic markers. Alternately, suppose purified forms of the tumor marker are amply stable to permit the preparation of calibration standards to facilitate accurate quantitation. In that case, chromatographic methods may be developed to identify and measure the tumor marker in biological specimens.
