SCINTIGRAPHIC DETECTION OF MELANOMA METASTASES WITH A RADIOLABELED BENZAMIDE ([IODINE-123]-(S)-IBZM)

droxy-3-iodo-6-methoxy-N-[(1-ethyl-2-pyrrolidinyl) methyl] benzamide ( [I-123]-(S)-IBZM) is a radiolabeled benzamide usually employed to stud y neuropsychiatric disorders, such as schizophrenia and Parkinson's di sease. The ectodermic origin of melanocytes and the presence of melani n in the substantia nigra are the theoretic basis of the experimental use of this class of tracers for melanoma imaging. Methods: Eleven pat ients with proven metastatic melanoma entered the study. Whole-body an d planar scintigrams were performed 2, 4 and 24 hr after intravenous i njection of a mean tracer activity of 205 MBq. The dosimetric evaluati on was performed by the Medical Internal Radiation Dose Committee meth od. Results: The [I-123]-(S)-IBZM scans allowed the detection of all s ix cutaneous lesions, five of six superficial pathologic lymph nodes, four of five pulmonary and one of two hepatic metastases. The maximum tumor-to-background ratio was 2.6 in planar images. The hepatobiliary excretion of the tracer may limit detection of intra-abdominal lesions . Dosimetry is similar to data for nononcologic patients. Conclusion: Although it is unclear if the mechanism of radiopharmaceutical uptake in melanoma is due to binding to membrane receptors or due to interact ions with intracellular structures, radiolabeled benzamide is a promis ing tracer to detect melanoma.