Role of PET in medullary thyroid carcinoma.
In the diagnostic assessment of medullary thyroid carcinoma (MTC), nuclear medicine imaging provides its contribution mainly in the postoperative work-up to detect residual or recurrent tumor. With respect to scintigraphy with gamma-emitter radiopharmaceuticals, positron emission tomography (PET) offers interesting perspectives owing to its higher image quality, spatial resolution and speed. Moreover, the recent developments of hybrid machines allow to obtain images that simultaneously hold both anatomic (computed tomography) and functional (PET) information with great impact on diagnostic efficacy. (18)F-fluoro-deoxyglucose ((18)F-FDG) is the most frequently used PET tracer in oncology. Preliminary reports of FDG-PET in MTC patients show encouraging results with a higher sensitivity in detecting local recurrent and metastatic disease when compared with single photon emission tracers. However, (18)F-FDG uptake depends on lesion size and to some extent on the grade of differentiation and biologic aggressiveness of the tumor; so FDG-PET seems useful mainly in patients with very high calcitonin levels and high progression rate. Like other neuroendocrine tumors, MTC is characterized by the presence of amine uptake mechanism and/or peptide receptors at the cell membrane allowing the clinical use of specific radiopharmaceuticals that reflect the different metabolic pathways of MTC, and in particular the synthesis, storage and release of hormones ((18)F-dihydroxyphenilalanine, (18)F-DOPA and (18)F-fluorodopamine, (18)F-FDA) and the expression of receptors ((68)Ga-labeled somatostatin analogs). These tracers are currently under investigation and will further improve the diagnostic approach of MTC.
Rufini
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Institute of Nuclear Medicine, UniversInstitute of Nuclear Medicine, Università Cattolica del Sacro Cuore, Rome, Italy. v.rufini@rm.unicatt.it
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Perotti
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Leccisotti
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Calcagni
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D018276:Carcinoma, Medullary / Q000000981:diagnostic imaging*; D019788:Fluorodeoxyglucose F18; D006801:Humans; D049268:Positron-Emission Tomography / Q000379:methods; D019275:Radiopharmaceuticals; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013964:Thyroid Neoplasms / Q000000981:diagnostic imaging*
D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18