If an antibody can be prepared which is capable of recognizing tumor cells, but has little or no cross-reaction to any normal human tissue, it may be suitable for scanning. In principle a radioactive isotope may be attached to a monoclonal antibody is such a fashion that the immunoreactivity of the antibody, as defined by in vitro biding assays, is unaltered. If such a labelled antibody is then injected into the patient, after a suitable time the antibody will bind to tumor associated antigens in the patient. The localization of this antibody-antigen complex can be detected by an external radiation camera and an image produced of the patient's body outline with the position of the labelled antibody-antigen complexes. It is correct to think of such scans as antigen distribution images where the molecule being imaged is in fact the tumor-associated antigen.
