Medullary Thyroid Carcinoma presenting as an Incidentaloma on Gallium-68-PSMA-PET/CT - Systematic Literature Review and Case Report.

The prostate-specific membrane antigen (PSMA) is established in imaging and treatment of prostate cancer, especially in recurrent disease. PSMA is a membranebound glycoprotein with the function of a glutamic acid releasing carboxypeptidase enzyme, which is biologically expressed by the prostate and among others, proximal renal tubule cells, small intestine, central and peripheral nervous system [1]. Positrone Emission Tomography (PET)/ Computed Tomography (CT) imaging with Gallium (Ga)-68 in prostate cancer has its benefits in demonstrating the extent of the current disease and in preceding possible therapy with radionuclides like Lutetium (Lu)-177 and also the feasibility of intraoperative probe-assisted detection and localization of respective lesions. Numerous immunohistochemical studies have shown that PSMA is also upregulated on the endothelial cells of the neovasculature of a diverse group of other solid tumors. PSMA appears to promote endothelial invasion cell proliferation through its regulation of lytic proteases that can cleave the extracellular matrix [2]. PSMA expression in the neovasculature of tumors was likewise shown for example in renal cell carcinoma, rectal carcinoma, lung cancer, hepatocellular carcinoma, lymphoma, urinary bladder, stomach, small intestine and differentiated thyroid cancer [3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14]. Heitkötter et al discussed that in thyroid carcinomas, PSMA expression was more common in poorly differentiated species [15]. Poorly differentiated tumors grow rapidly, resulting in intratumoral hypoxemia, in which PSMA supports neovascularization. It is therefore not surprising that several studies have demonstrated an association between high PSMA expression and poorer prognosis and outcome. Haffner et al. were able to demonstrate this association in squamous cell carcinoma of the oral cavity, Jiao et al. in hepatocellular carcinoma and Sollini et al. in differentiated thyroid cancer [16, 17, 18].