Two peptide receptor ligands 99mTc-EDDA/HYNIC-Tyr3-octreotide and 99mTc-EDDA/HYNIC-DGlu-octagastrin for scintigraphy of medullary thyroid carcinoma

Somatostatin and gastrin receptors are overexpressed in medullary thyroid carcinoma (MTC) cells; hence, both of them are potential targets for peptide receptor scintigraphy and radiotherapy. Therefore, the aim of our study was to assess the clinical value of two technetium-99m-labeled peptides, a new gastrin analog, the EDDA/HYNIC-(D)Glu-octagastrin and a somatostatin analog, EDDA/HYNIC-Tyr(3)-octreotide (EDDA/HYNIC-TOC)for scintigraphy in patients with MTC to detect recurrences and metastases and select patients for peptide receptor radiotherapy. Material and Methods: Thirty (30) patients, 20 females and 10 males, 22-83 years of age (mean, 52.7) with the diagnosis of MTC in different stages of the disease (preoperative, postsurgery, remission, recurrence, or metastatic disease) were included in this study. Before surgery, in all patients serum calcitonin concentrations were elevated. The diagnosis of MTC was confirmed in all cases by histopathology of the removed tumor and immunohistochemical staining giving positive reactions for calcitonin and chromogranin A. Imaging studies using Tc-99m-EDDA/HYNIC-TOC and a new minigastrin analog, Tc-99m-EDDA/HYNIC-(D)Glu-octagastrin, were performed in each patient and the results compared with each other and with other imaging methods. Scans of the whole body, head, neck, and chest were performed 2 and 4 hours after injections of the trace; 500-600 MBq in each case, using a double-head Varicam (Elscint, Israel) gamma camera. Results: 99mTc-EDDA/HYNIC-TOC detected somatostatin receptor positive lesions in 20 patients with MTC whereas Tc-99m-EDDA/HYNIC-(D)Glu-octagastrin displayed gastrin receptors in 11 patients. In 9 cases, the scans were positive in both methods, although in 2 cases different pathologic foci were visualized. In 12 cases, only Tc-99m-EDDA/HYNIC-TOC scintigraphy was positive, whereas in 3 other cases only Tc-99m-EDDA/HYNIC-DGlu-octagastrin revealed pathologic lesions. Conclusions: Scintigraphy using Tc-99m-HYNIC-TOC permits the visualization of somatostatin receptor positive MTC in the majority of cases. The new gastrin analog, Tc-99m-HYNIC-(D)Glu-octagastrin, is well tolerated, shows no renal retention, and in some cases of MTC provides additional information on the expression of gastrin receptors. However, inferior quality of octagastrin scans indicates the need for further improvement of this radiopeptide.