title: Factors predicting tracer uptake in somatostatin receptor and MIBG scintigraphy of metastatic gastroenteropancreatic neuroendocrine tumors.
abstract: Radiolabeled octreotide analogs (Oct) and metaiodobenzylguanidine (MIBG) offer 2 different approaches for imaging and targeting metastatic gastroenteropancreatic neuroendocrine tumors (GEP-NET). Despite successful establishment of the revised World Health Organization (WHO) classification, which distinguishes between low- and high-grade malignant GEP-NET, there is a lack of scintigraphic studies comparing uptake behavior on the basis of this categorization. This study aims to define predisposing factors of tracer uptake for both imaging principles implementing the updated tumor criteria of the current WHO classification.
  
  
  METHODS
  Fifty-seven consecutive patients with histologically confirmed metastatic GEP-NET evaluated with both 111In-pentetreotide and 123I/131I-MIBG scintigraphy were included in this study. Intensity of tracer uptake was graded according to the different metastatic regions. Patients were classified as overall positive when avid uptake in the clinically relevant tumor lesions was present. Correlation was tested between the proportion of positive patients and tumor origin, function, and malignancy.
  
  
  RESULTS
  Overall, 52 patients (91.2%) were Oct positive and 28 patients (49.1%) were MIBG positive. The proportion of tracer-positive patients was significantly higher (P < 0.05) in low-grade malignant tumors for both tracers and in functioning as well as in gastroenteral NET for MIBG. Five patients were negative for both tracers. None of the Oct-negative patients proved to be MIBG positive.
  
  
  CONCLUSIONS
  Oct affinity is observed with high frequency throughout the subgroups of metastatic GEP-NET, whereas corresponding MIBG uptake is overall less prevalent and more group dependent. Tumor differentiation significantly impacts both Oct and MIBG uptake, whereas functionality predisposes only for MIBG accumulation. Though clearly inferior to Oct-based radioimaging in most GEP-NET, MIBG achieves a remarkable rate of radioligand accumulation in functioning midgut enterochromaffin cell metastases (>80% of patients positive). These results may have implications for patient management and potentially for selection and performance of targeted therapy.
authors.affiliation: Department of Nuclear Medicine, University of Bonn, Bonn, Germany. samer.ezziddin@ukb.uni-bonn.de
authors.forename: Samer
authors.initials: S
authors.lastname: Ezziddin
authors.forename: Timur
authors.initials: T
authors.lastname: Logvinski
authors.forename: Charlotte
authors.initials: C
authors.lastname: Yong-Hing
authors.forename: Hojjat
authors.initials: H
authors.lastname: Ahmadzadehfar
authors.forename: Hans-Peter
authors.initials: HP
authors.lastname: Fischer
authors.forename: Holger
authors.initials: H
authors.lastname: Palmedo
authors.forename: Jan
authors.initials: J
authors.lastname: Bucerius
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Reinhardt
authors.forename: Hans-Jürgen
authors.initials: HJ
authors.lastname: Biersack
mesh_terms: D019797:3-Iodobenzylguanidine / Q000493:pharmacokinetics*; D000328:Adult; D000368:Aged; D004067:Digestive System Neoplasms / Q000000981:diagnostic imaging / Q000378:metabolism* / Q000556:secondary*; D005260:Female; D005770:Gastrointestinal Neoplasms / Q000000981:diagnostic imaging / Q000378:metabolism / Q000556:secondary; D006801:Humans; D008297:Male; D008875:Middle Aged; D018358:Neuroendocrine Tumors / Q000000981:diagnostic imaging / Q000378:metabolism* / Q000556:secondary*; D010190:Pancreatic Neoplasms / Q000000981:diagnostic imaging / Q000378:metabolism / Q000556:secondary; D011379:Prognosis; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D017481:Receptors, Somatostatin / Q000378:metabolism*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013004:Somatostatin / Q000031:analogs & derivatives* / Q000493:pharmacokinetics
chemical_list: D019275:Radiopharmaceuticals; D017481:Receptors, Somatostatin; D019797:3-Iodobenzylguanidine; D013004:Somatostatin; C081788:pentetreotide