IMMUNOSCINTIGRAPHY OF TUMORS USING TC-99(M)-LABELED MONOCLONAL-ANTIBODIES - A REVIEW

Tc-99m is the optimum radionuclide for imaging in nuclear medicine due to its superior physical properties (Egamma of 140 keV and t1/2 of 6 h). Several techniques have recently been developed for labelling mono clonal antibodies with Tc-99m for immunoscintigraphy of human malignan cies. These techniques primarily consist of either direct labelling of endogenous sulphydryl groups on the immunoglobulin with Tc-99m or ind irect labelling through conjugation of a preformed Tc-99m-chelate. Dir ect methods offer the best promise for a one-step labelling kit but th e Tc-99m-antibody may be unstable in vivo. This instability has been a dvantageous, however, in reducing blood background radioactivity and a chieving sufficiently high tumour/blood ratios for clinical imaging. O ver 1200 patients have been studied with Tc-99m-labelled monoclonal an tibodies in the past decade. The majority of studies have been carried out in melanoma or colon cancer but other malignancies have also been investigated. The sensitivity has been variable and depended both on the size of the lesion and its location. Single photon emission comput ed tomographic imaging was helpful in some instances. Further study of labelling techniques and their effect on the pharmacokinetics of Tc-9 9m-labelled monoclonal antibodies as well as additional clinical evalu ation of these agents is indicated.