Early studies of immunoscintography with affinity-purified 131I-labeled polyclonal
antibodies reactive against
oncofetal antigens such as
carcinoembryonic antigen (CEA) were moderately successful in detecting metastatic
colorectal carcinoma. However, because of low
tumor to background ratios of
isotope, background subtraction techniques using 99Tc-labeled
albumin were required to visualize small lesions.
Antisera were often of low titer and lacked specificity. These problems could be overcome for the most part following the development of highly specific
monoclonal antibodies (MoAb) against a variety of
tumor-associated
antigens. A number of clinical trials using 131I- or 111In-labeled MoAb to image
tumors have demonstrated successful localization without the use of subtraction techniques. Variables limiting the usefulness of murine MoAb for diagnosis have included increased localization in liver and spleen,
tumor vascularity and heterogeneity of
antigen expression, and development of human antimurine
globulins. Methods to overcome some of these problems are discussed. Radiolabeled MoAb appear useful as an adjunct to conventional diagnostic techniques both as a means to predict which
antibodies might be useful for treatment and, in select patients, as a basis for treatment decisions.