Preclinical and clinical testing of radiolabelled monoclonal antibodies for immunoscintigraphy

: Immunoscintigraphy is a new method for in vivo diagnosis of diseases using monoclonal antibodies. Emphasis is placed on diagnosis of malignant tumors although the range of application includes a number of non-malignant diseases. To date, no European country has issued clear guidelines on the testing and registration of those monoclonal antibodies labelled with a radionuclide and used for diagnostic. This involves the risk of overregulation which would considerably reduce the applicability of the method. This holds particularly true since the complications initially anticipated with the use of such compounds did not occur. The conduct of immunoscintigraphy has evolved during the last few years. For reasons of applicability, but also and mainly for reasons of radiation hygiene, I-131 and finally also In-111 were abandoned as labelling nuclides and replaced by Tc-99m. The protein amount involved was reduced. Some false estimations, which were due to particularities or artifacts of the iodinated antibodies used at the beginning, had to be corrected: the representation of the liver in a scintigram is part of the physiological distribution of antibodies; and fragments of antibodies normally do not present the anticipated kinetic advantages. The clinical results obtained with colon carcinomas show that not only recurrencies and metastases, but also primary tumors can be detected with equally high sensitivity. In contrast, radioimmunotherapy does not yet seem as successful, at least against solid tumors.