Radioguided surgery with radiolabeled somatostatin analogs: not only in GEP-NETs

Radioguided surgery (RGS) is a surgical technique that, using intra-operative probes, enables the surgeon to identify tissues preoperatively "marked" by a radiopharmaceutical. Somatostatin receptors (SSTRs) are present in the majority of neuroendocrine cells and may be over-expressed not only by tumor cells, but also by endothelial cells of peritumoral vessels, inflammatory cells and cells of the immune system, such as activated lymphocytes, monocytes and epithelioid cells. This extra neoplastic uptake is the rationale for the use of radiolabeled somatostatin analogs (SSAs) either in some tumors not expressing SSTRs or in various non-oncological diseases. The crucial point of RGS technique lays in the establishment of a favorable tumor-to-background ratio (TBR). A wide range of probe systems are available with different detectors and many radiopharmaceuticals have been experimented and utilized, mainly using g-detection probes; in order to widen RGS application field, newer approaches with b- or b+ emitting radioisotopes have also been proposed. Together with the consolidated clinical use, a promising and effective employment of RGS may be found in neuroendocrine tumors (NETs) using 111In-pentetreotide (OCT). RGS with OCT has been demonstrated useful in the management of patients with gastroenteropancreatic (GEP) tumors, lung, brain and breast cancer. Preoperative scintigraphy or PET with DOTA-peptides combined with RGS increases the rate of successful surgery. Preliminary studies with b- probes using 90Y-SSA suggest the possible interest of this approach in patients undergoing peptide receptor radiotherapy.