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-131), F-18-FDG PET, and Ga-68-PSMA-HBED-CC PET scans as per the institution protocol. PSMA expression (SUVmax) was compared with F-18-FDG and I-131 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-68-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.