Intraoperative use of gamma-detecting probes to localize neuroendocrine tumors

Neuroendocrine tumors are characterized by the expression of different pept ides and biogenic amines. These rare tumors tend to grow slowly and are not oriously difficult to localize, at least in the early stages. Surgical remo val is the only definitive therapeutic option for neuroendocrine tumors and relief from hyperfunctional status. The effectiveness of surgical treatmen t is invariably dependent upon the complete surgical excision of all tumor tissue, because microscopic and occult disease not readily seen by the surg eon may remain in situ, leading to shortened survival. Therefore, pre- and intraoperative localization of the primary as well as of metastatic tumors is of utmost importance. Radioguided surgery (RGS) is an intraoperative tec hnique that enables the surgeon to localize radiolabelled tissue based on t he characteristics of the various tissues. Concerning gastroenteropancreati c tumors (GEP), intraoperative gamma probe examination is able to reveal sm all tumor sites accumulating (In-111-DTPA-D-Phe(1))-pentetreotide more effi ciently (>90%) than somatostatin receptor scintigraphy (68%-77%), because l esions with a size smaller than 5 mm in greatest dimension could be identif ied. Furthermore, RGS identified 57% more lesions when compared to the "pal pating finger" of the surgeon. In medullary thyroid cancer (MTC), surgical removal of the tumor is the first and most efficient treatment of the disea se. Persistent or increasing serum calcitonin and carcinoembryonic antigen (CEA) levels imply tumor recurrence after thyroid ablation. For imaging rec urrent MTC many radiopharmaceuticals have been used to visualize tumor site s, but none of them has shown excellent sensitivity. Preoperative somatosta tin receptor scintigraphy and intraoperative RGS in patients with recurrent MTC demonstrate only part of the tumor sites and cannot visualize small tu mor sites (less than 10 mm). In comparison, RGS using Tc-99m(V)-DMSA detect s metastases with a size of 5 mm in diameter, whereas the "palpating finger " of the surgeon localized metastases with a size of more than 1 cm in diam eter. In patients with recurrent MTC, intraoperative gamma probe examinatio n is able to localize over 30% more tumor lesions when compared with conven tional preoperative imaging. modalities and surgical findings. MIBG scintig raphy is the most sensitive technique for the detection and staging of neur oblastoma (sensitivity 92%; specificity nearly 100%). Intraoperative RGS wi th iodine labelled MIBG has been developed to improve the definition of tum or Limits or to localize small, nonpalpable tumors. Comparison of I-123- an d I-125-labelled MIBG revealed a sensitivity of 91% and 92%, respectively; the specificity of I-125 (85%) was significantly higher than that of I-123 (55%). In addition to scintigraphy of the adrenal glands by precusors of ad renal hormones, imaging with a radiolabelled somatostatin analogue is possi ble; however, (In-111-DTPA-D-Phe(1))-pentetreotide is not specific for any adrenal disease or function and the relatively high radioligand accumulatio n in the kidneys limited the use for detection of tumors in the area of the adrenal glands.