SOMATOSTATIN RECEPTOR SCINTIGRAPHY WITH [IN-111-DTPA-D-PHE(1)]- AND [I-123-TYR(3)]-OCTREOTIDE - THE ROTTERDAM EXPERIENCE WITH MORE THAN 1000 PATIENTS

Various tumours, classically specified as either neuroendocrine or non -neuroendocrine, contain high numbers of somatostatin receptors, which enable in vivo localization of the primary tumour and its metastases by scintigraphy with the radiolabelled somatostatin analogue octreotid e. In addition granulomas and autoimmune processes can be visualized b ecause of local accumulation of somatostatin receptor-positive activat ed mononuclear leucocytes. In many instances a positive scintigram pre dicts a favourable response to treatment with octreotide. It is tempti ng to speculate that octreotide labelled with an appropriate radionucl ide might be used in cancer therapy. The successful application of rad iolabelled octreotide in scintigraphy indicates the possible usefulnes s of other radiolabelled peptides, either native peptides or derivativ es of these, in, for example, nuclear oncology. The small size of thes e peptides, e. g. bombesin and substance P, is of the utmost importanc e for a relatively fast blood clearance, thus leading to low backgroun d radioactivity. In this way peptides are powerful alternatives to (fr agments of) monoclonal antibodies, the application of which to scintig raphic localization of specific cell surface antigen-bearing tumours i s plagued by slow blood clearance and, hence, high background levels.