Prostate-Specific Membrane Antigen Expression in Patients With Differentiated Thyroid Cancer With Thyroglobulin Elevation and Negative Iodine Scintigraphy Using 68Ga-PSMA-HBED-CC PET/CT.

PURPOSE OF THE REPORT: Prostate-specific membrane antigen (PSMA) is a member of superfamily of zinc-dependent exopeptidases that is robustly expressed in prostate cancer cells and nonprostatic solid tumor neovasculature including microvessels of thyroid tumors. Its expression in differentiated thyroid cancer (DTC) has been confirmed in many recent studies, but systematic studies exploring PSMA expression in patients with DTC with thyroglobulin elevation and negative iodine scintigraphy (TENIS) are lacking. The aim of the present study was to evaluate the role of PSMA scan in TENIS patients with DTC. METHODS: Nine consecutive patients with DTC with proven TENIS syndrome (6 men and 3 women with age range 29-68 years and mean age of 48 years) underwent 18F-FDG PET/CT as per the institution protocol. Thereafter, they were subjected to 68Ga-PSMA-HBED-CC PET/CT as per the institution protocol within a week of FDG PET imaging. Prostate-specific membrane antigen expression (SUVmax) in the lesions was compared with 18F-FDG PET and CT scan findings. RESULTS: In 5 of 9 patients with TENIS, the metastatic lesions showed PSMA expression. A total of 14 lesions were seen on the CT scan. Prostate-specific membrane antigen PET detected 9 of 14 lesions (64.28%) (SUVmax ranging from 10.1 to 45.67; median SUVmax of 16.31), whereas FDG PET was positive in 11 of 14 lesions (78.57%). The lesions that showed PSMA uptake was localized to bones (5 of 9) and lungs (4 of 9). Two lesions that were localized to iliac crest and acetabulum were missed on FDG PET but were seen on CT and PSMA PET scan. CONCLUSIONS: The results of this pilot study indicate that 68Ga-HBED-CC-PSMA PET/CT demonstrates PSMA expression in TENIS patients with lesions being localized to the bones and lungs. 68Ga-PSMA PET/CT could be useful for the identification of TENIS patients who might benefit from PSMA-targeted radionuclide therapy.

Evidence of Prostate-Specific Membrane Antigen Expression in Metastatic Differentiated Thyroid Cancer Using 68Ga-PSMA-HBED-CC PET/CT.

PURPOSE OF THE REPORT: Prostate-specific membrane antigen (PSMA) overexpression is not restricted to prostate cancer, but it has also been demonstrated in gliomas, lung cancer, and in tumor neovasculature. Systematic studies exploring PSMA uptake in thyroid tumors are lacking. The aim of this pilot study was to assess PSMA expression in patients with metastatic differentiated thyroid cancer (mDTC). MATERIALS AND METHODS: Ten patients of mDTC harboring 32 lesions (5 men; age range, 38-65 years; mean age, 50 years) underwent prospective evaluation with radioiodine (I), F-FDG PET, and Ga-PSMA-HBED-CC PET scans as per the institution protocol. PSMA expression (SUVmax) was compared with F-FDG and I scan findings in all patients. RESULTS: Lesions were radioiodine avid in 8 patients, whereas 2 were classified as thyroglobulin elevation with negative iodide scintigraphy (TENIS) patients. All patients with iodine-avid metastatic disease showed substantial PSMA uptake. PSMA PET detected 30/32 total lesions (93.75%; SUVmax ranging from 4.86 to 101.81 with median SUVmax of 31.35), whereas FDG PET/CT was positive in 23/32 lesions (81.85%). Twenty-one (70%) of 30 lesions that showed PSMA expression were localized to the bones. PSMA localized a lesion in each of the 2 TENIS patients similar to FDG PET scan. CONCLUSIONS: Ga-PSMA-HBED-CC PET/CT is a potentially useful imaging modality in patients of mDTC with most (70%) of PSMA expressing metastasis being localized to the bones. PSMA PET/CT could be useful for identifying patients with limited therapeutic options (eg, TENIS) who might benefit from PSMA-targeted radionuclide therapy.