^99mTc-Demogastrin 2 for CCK-2 receptor scintigraphy in medullary thyroid carcinoma

Objectives In medullary thyroid carcinoma (MTC) serum calcitonin is a very sensitive and specific tumor marker. However, localization of recurrent tumor or metastases is often not possible with presently available diagnostic imaging modalities. MTC often (>90%) overexpresses cholecystokin-2 receptors (CCK2R), these might be viable targets for radionuclide scintigraphy. Results of ^99mTc-N₄-Gly-(D)Glu-(Glu)₅-Ala-Tyr-Gly-Trp-Met-Asp-Phe-NH₂ (^99mTc-Demogastrin 2) scintigraphy in patients (pts) with primary MTC (preoperatively) and pts with elevated serum calcitonin levels after neck surgery are reported.

Methods 32 pts (21 female; age 17-76 y, median 43 y) were studied, 3 preoperative. 17 pts had elevated calcitonin levels but no known tumor localization. Scintigraphy was performed at 3-4 and/or 8 and/or 24 h post injection of ± 800 MBq ^99mTc-Demogastrin 2.

Results 15 pts had known tumor localizations; with exception of a pt with only small liver metastases (3 mm which scan equivocal), the radionuclide scan of all these pts was judged positive. In 8 of them additional lesions were found. Of 17 pts without known tumor lesions 9 pts had positive lesions in neck, mediastinum/lung-hilum, bone, lung and/or liver. In 7 of these 9 pts at least 1 lesion was confirmed with CT, MRI and/or ultrasound. The smallest positive neck lesion was 2.9 mm (cytology showed MTC). In 2 pts lesions have not yet been confirmed. In 2 pts non-visualized neck lesions were subsequently discovered by other means and resected; in-vitro autoradiography of these metastases showed lack of clear CCK2R overexpression.

Conclusions Total body CCK2R imaging with ^99mTc-Demogastrin 2 can be helpful to localize MTC metastases as even very small metastases (< 5 mm) and lesions at unexpected locations could be visualized. Further studies are needed to define its value in patient management