Abstract
Prostate-specific membrane antigen (PSMA; also termed glutamate carboxypeptidase II (GCP II)) is abundantly expressed in prostate cancer. It has been shown recently that PSMA is expressed in neovasculature of differentiated thyroid cancer. In this study, we show that (18)F-DCFPyl might detect neovasculature in advanced, metastatic differentiated thyroid cancer (DTC). We first stained the preserved lymph node samples of three patients with DTC who had undergone total thyroidectomy and neck dissection for cervical lymph node metastatic disease to identify PSMA expression, with the PSMA antibody (DAKO Monoclonal). Then, we performed (18)F-DCFPyl imaging in two other advanced DTC patients with elevated serum thyroglobulin (Tg), indicative of residual disease. We compared the findings with contemporaneous FDG PET/CT scan, conventional Imaging (CT,MRI) and whole-body scan performed with I(123)/I(131). All the three lymph node samples stained positive for PSMA expression in the neovasculature. In the first imaged patient, (18)F-DCFPyl detected activity within the retropharyngeal CT contrast-enhancing lymph node. Compared to FDG PET/CT, the (18)F-DCFPyl scan showed a greater SUV (3.1 vs 1.8). In the second imaged patient, (18)F-DCFPyl showed intense uptake in the L3 vertebra (not seen on the post treatment (131)I scan or the (18)F-FDG PET/CT). MRI of the lumbar spine confirmed the presence of sclerotic-lytic lesion at the location, consistent with metastatic disease. Our exploratory study is proof of principle, that the prostate cancer imaging agent (18)F-DCFPyl may prove useful for the localization of metastases, in patients with metastatic RAI-refractory DTC by detecting neoangiogenesis within the tumor.