Clinical role of positron emission tomography (PET) in endocrine tumours

Positron emission tomography (PET) is considered one of the most effective nuclear medicine imaging modality in oncology. In many types of malignant tumours PET has proven to be high sensitive in detecting both primary neoplasm and metastatic disease both before therapy for staging purposes and after surgery, radiotherapy and chemotherapy during follow-up. In particular, PET showed high accuracy in differentiating post-treatment scar from viable tumoural tissue and high sensitivity in visualising very small metastatic foci as those in normal-sized (less than 1 cm in diameter) lymph nodes. A large variety of positron emitter tracers have been produced for PET imaging: the most widely used tracer in clinical oncology is 18F-fluoro-2-deoxy-D-glucose (18F-FDG). Deoxy-glucose (DG) is a glucose analog that enters the cell using specific transmenbrane carrier proteins (especially GLUT-1). Once within the cytoplasm, DG is phosphorylated to FG-6-phosphate but does not appear to be further metabolised. In most malignant tumours there is an increase of the glycolityc metabolism which accounts for an increase of the FDG uptake. However, the metabolic cellular activity can be only slightly increased or even normal in well differentiated and slow growing tumours as some endocrine neoplasms. In the present review, the clinical usefulness and limits of PET imaging are discussed in the management of patients with endocrine tumors.