Imaging of PSMA expression in metastatic differentiated thyroid cancer using 68Ga-HBED-CC-PSMA PET/CT

Objectives The prostate-specific membrane antigen (PSMA), which was originally thought to be specific for prostate carcinoma, was recently shown to be overexpressed on endothelial cells of the neovasculature of several malignancies. Here, we evaluate the role of 68Ga-HBED-CC-PSMA (68Ga-PSMA) PET/CT for the detection of PSMA expression in patients with metastasized differentiated thyroid cancer (DTC).

Methods Six patients with iodine-negative and [18F]-fluorodeoxyglucose (FDG)-positive metastasized DTC (mean TG: 1906.2 ng/ml) received 80 ± 9 MBq of the 68Ga-labeled PSMA ligand and underwent PET/CT at 62 ± 7 min p.i.. Data were analyzed regarding the tumor accumulation capacity of the tracer and the detection rate of local recurrences and metastases compared to [18F]-FDG. Tracer uptake was quantified in terms of the maximal standardized uptake value (SUVmax) within a spheroidal volume of interest (VOI). A characterization for malignancy was made in consensus taking into account existing prior examinations.

Results In 5/6 patients, sites of putative metastatic disease could be identified using 68Ga-PSMA PET/CT. All lesions detected with 68Ga-PSMA PET/CT (n=42) were confirmed by [18F]-FDG-PET/CT or conventional CT imaging. The tumor lesions detected included local recurrences (n=2), lymph node lesions (n=24), bone lesions (n=11) as well as soft-tissue metastases (n=5). Using 68Ga-PSMA PET/CT, all tumor lesions identified with [18F]-FDG-PET/CT imaging could be visualized in 3/5 patients. In 2 patients, only the most prominent lesions detected with [18F]-FDG-PET/CT imaging were visualized with the PET component of 68Ga-PSMA PET/CT. 68Ga-PSMA uptake ranged from low in 1 patient (mean SUVmax 3.3) to intermediate (1 patient, mean SUVmax 6.1) to intense (3 patients, mean SUVmax 12.8, 16.2 and 18.3). The highest SUVmax were observed for a bone lesion, reaching 39.7. In 1 patient, no 68Ga-PSMA uptake was observed.

Conclusions These preliminary results indicate that 68Ga-PSMA PET/CT is suitable for staging of patients with metastasized DTC. 68Ga-PSMA PET/CT could be useful for the identification of patients that might qualify for PSMA-based endoradiotherapy due to high PSMA uptake.