18F-FLT and 18F-FDG positron emission tomography for the imaging of advanced well-differentiated gastro-entero-pancreatic endocrine tumours.

Purpose: Gastro-entero-pancreatic (GEP) endocrine tumours are a heterogenous group of tumours of variable localization and prognosis. It has been suggested that positron emission tomography (PET) using 2-[18F]fluoro-2-deoxy-D-glucose (18F-FDG) may have a prognostic value and help to identify patients at risk of progression. [18F]fluoro-3'-deoxy-3'-L-fluorothymidine (18F-FLT) has been recently developed as a PET proliferation tracer. At present, there are no studies investigating its role in GEP. The aim of this prospective study was to assess the value of 18F-FLT-PET for the evaluation of GEP.

Materials And Methods: Ten patients with biopsy-proven locally advanced or metastasized, well-differentiated GEP neuroendocrine tumours were prospectively enrolled and scheduled for 18F-FDG and 18F-FLT-PET. Images were compared with other conventional diagnostic procedures, namely computed tomography, ultrasound, somatostatin receptor scintigraphy and with clinical and diagnostic follow-up.

Results: Evaluation criteria were interpreted in terms of assumed presence of tumoral tissue. According to the patient's status, FDG was positive in five out of the seven patients with stable disease and in two out of the three patients with progressive disease. No positive case was identified by 18F-FLT in either the primary or the metastatic tumour site, whatever the status of patients, and this was probably a reflection of the slow proliferation rate of tumours.

Conclusion: These preliminary data suggest that 18F-FLT-PET is not a suitable tracer for the evaluation of advanced well-differentiated GEP tumours. FDG showed good diagnostic performance but does not help to identify patients at risk of progression.