The New Radiolabeled Peptide (99m)TcEDDA/HYNIC-TOC: Is It a Feasible Choice for Diagnosing Gastroenteropancreatic NETs?

SIMPLE SUMMARY: Gastroenteropancreatic neuroendocrine tumors are a group of heterogenous tumors that account for about 60% of the neuroendocrine tumors diagnosed nowadays. They possess the capability to synthesize and secrete peptides and hormones that lead to their characteristic syndromes. One of their main characteristics is the expression of somatostatin receptors, which makes them appropriate for diagnosis based on radiolabeled somatostatin analogs scintigraphy and PET/CT. This retrospective monocentric study was conducted to determine the suitability of (99m)TcEDDA/HYNIC-TOC scintigraphy in diagnosis and management of gastroenteropancreatic neuroendocrine tumors, in comparison with other available radiotracers. We examined 173 patients referred to our clinic for a (99m)TcEDDA/HYNIC-TOC scan and, based on the obtained results, we estimated the sensitivity, specificity, accuracy, and positive and negative predictive values of the method. Our results confirm the utility of (99m)TcEDDA/HYNIC-TOC in the management and follow-up of patients suffering from gastroenteropancreatic neuroendocrine tumors, especially in centers that do not benefit from PET/CT equipment or (68)Ga-DOTA-peptides. ABSTRACT: (1) Background: The aim of our study is to reveal the advantages and limitations of the use of (99m)TcEDDA/HYNIC-TOC (Tektrotyd(®), Polatom) in the diagnosis of gastroenteropancreatic neuroendocrine tumors and to compare our results with the values obtained for (111)In-pentetreotide and (68)Ga-DOTA-peptides, routinely used in medical practice. (2) Methods: This retrospective monocentric study included 173 patients with gastroenteropancreatic neuroendocrine tumors who underwent (99m)TcEDDA/HYNIC-TOC scans as part of their clinical management. The examination protocol included a whole-body scan acquired 2 h after the radiotracer’s administration, with the SPECT/CT performed 4 h post-injection. Physiological and abnormal uptake were established by two experienced physicians and, based on the obtained results, sensitivity, specificity, accuracy, positive predictive value and negative predictive value were calculated. (3) Results: Our method presented a sensitivity of 90.5%, a specificity of 71.9%, and an accuracy of 84.3%, with a positive predictive value of 86.7% and a negative predictive value of 78.8%. (4) Conclusions: (99m)Tc-EDDA/HYNIC-TOC, a receptor-based radiopharmaceutical, could represent a competitor for (68)Ga-labeled peptides in the diagnosis and management of patients with gastroenteropancreatic neuroendocrine tumors. Our results show a lower sensitivity (90.5%) than (68)Ga-DOTA-peptides, but with great specificity, accuracy, positive, and negative predictive values.