In situ radiotherapy with In-111-pentetreotide - State of the art and perspectives

In-111-pentetreotide (Octreoscan(R)) and other radiolabeled somatostatin an alogs are useful in the management of well differentiated neuroendocrine ma lignancies such as carcinoid or islet cell neoplasms. These radiopeptides b ind to membrane bound somatostatin receptors (sst 1-5) which are over-expre ssed in a wide variety of neoplasms, especially those arising from the neur oectoderm. imaging advances allow for the noninvasive determination of the presence of sst receptors by combining radioactivity [(111)Indium with a so matostatin analog, DTPA-D-phe(1)-octreotide (pentetreotide)]. Radiolabeled somatostatin analogs bind to membrane receptors and internalization of the complex occurs. Auger emitting somatostatin analogs offer a novel and signi ficantly less toxic approach to controlling neoplastic diseases by deliveri ng targeted radiation specifically to receptor bearing cells while sparing receptor negative cells, Responses of 62-69% in 85 patients with metastatic neuroendocrine tumors treated with high dose (6-19.6 GBq) In-111-pentetreo tide, specifically targeting tumor somatostatin receptors, have been report ed. Objective responses observed included biochemical and radiographic resp onses with prolonged survival. This article will discuss and review the mul ti-center data available to date, the mechanisms of action of radiolabeled somatostatin analogs, dosimetry, clinical response parameters, and toxicity .