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

Abstract

(1) Background: The aim of our study is to reveal the advantages and limitations of the use of ^99mTcEDDA/HYNIC-TOC (Tektrotyd^®, Polatom) in the diagnosis of gastroenteropancreatic neuroendocrine tumors and to compare our results with the values obtained for ¹¹¹In-pentetreotide and ⁶⁸Ga-DOTA-peptides, routinely used in medical practice. (2) Methods: This retrospective monocentric study included 173 patients with gastroenteropancreatic neuroendocrine tumors who underwent ^99mTcEDDA/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: ^99mTc-EDDA/HYNIC-TOC, a receptor-based radiopharmaceutical, could represent a competitor for ⁶⁸Ga-labeled peptides in the diagnosis and management of patients with gastroenteropancreatic neuroendocrine tumors. Our results show a lower sensitivity (90.5%) than ⁶⁸Ga-DOTA-peptides, but with great specificity, accuracy, positive, and negative predictive values.

Keywords: 68Ga-DOTA-peptides; 99mTcEDDA/HYNIC-TOC; gastroenteropancreatic neuroendocrine tumours; somatostatin analogs.

Figure 1

A 71-year-old female patient, diagnosed with a hepatic metastasis of neuroendocrine tumor of unknown origin (confirmed by biopsy, NET G1). The SPECT/CT images show the presence of the hepatic lesion (pink arrows), also showcasing the primary tumor in the ileum (red arrow). The histopathological exam performed after surgical excision of the mass confirmed the presence of a neuroendocrine tumor.

Figure 2

A 64-year-old male patient diagnosed with an ileal neuroendocrine tumor (NET G1), excized in 2021. The present SRS shows increased uptake corresponding to mesenteric lymphadenopathy ((a), red arrows) and multiple liver metastases (pink arrows), the most prominent one situated in the VIII hepatic segment (b), visible on the WB planar scan as well (c).

Figure 3

A 69-year-old female patient diagnosed with a pancreatic neuroendocrine tumor (confirmed through multiple biopsies from the pancreatic head and liver metastasis as NET G2), undergoing treatment with somatostatin analogs. The WB SRS revealed ^99mTc-EDDA/HYNIC-TOC uptake in the abdominal region (a), with the SPECT/CT showing SSTR-expressing liver metastases (b) and two foci of increased uptake in the pancreas: one corresponding to the tail of the pancreas (c) and one in the head of the pancreas (d).

Figure 4

A 69-year-old female patient who underwent ^99mTc-EDDA/HYNIC-TOC SRS for biochemical suspicion of NET (high values of seric Chromogranin A). The scan revealed increased uptake in the uncinate process of the pancreas (arrow). The histopathological examination from the subsequent excision of the mass proved to be negative for NET.

Figure 5

Comparison between ^99mTc-EDDA/HYNIC-TOC SPECT/CT (pink arrows) and ⁶⁸Ga-DOTATATE PET/CT (red arrows) in a 54-year-old female patient, diagnosed with a pancreatic neuroendocrine tumor (G2), with multiple liver, lymphatic, and osseous metastases. The patient underwent four sessions of ¹⁷⁷Lu-DOTATATE PRRT between the PET scan and the SPECT examination. A better resolution for the ⁶⁸Ga-DOTATATE study can be observed, highlighting its higher capacity to detect smaller hepatic lesions and bone metastases. However, similar results can be seen both on ^99mTc-EDDA/HYNIC-TOC SPECT/CT and ⁶⁸Ga-DOTATATE PET/CT for bigger lesions.