Scintigraphic detection of melanoma metastases with a radiolabeled benzamide ([iodine-123]-(S)-IBZM).

Abstract

Iodine-123-(S)-2-hydroxy-3-iodo-6-methoxy-N-[(1-ethyl-2-pyrrolidinyl) methyl] benzamide ([123I]-(S)-IBZM) is a radiolabeled benzamide usually employed to study neuropsychiatric disorders, such as schizophrenia and Parkinson's disease. The ectodermic origin of melanocytes and the presence of melanin in the substantia nigra are the theoretic basis of the experimental use of this class of tracers for melanoma imaging. Eleven patients with proven metastatic melanoma entered the study. Whole-body and planar scintigrams were performed 2, 4 and 24 hr after intravenous injection of a mean tracer activity of 205 MBq. The dosimetric evaluation was performed by the Medical Internal Radiation Dose Committee method. The [123I]-(S)-IBZM scans allowed the detection of all six 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. Although it is unclear if the mechanism of radiopharmaceutical uptake in melanoma is due to binding to membrane receptors or due to interactions with intracellular structures, radiolabeled benzamide is a promising tracer to detect melanoma.