CARATTERIZZAZIONE DI LESIONI DI ORIGINE SCONOSCIUTA SOSPETTE PER LESIONI MALIGNE NEI PAZIENTI PEDIATRICI: POSSIBILE RUOLO DEL 18F-FDG PET/CT A.Cistaro 1,, E. Basso 2, R. Laudati 2, M. Bianchi 2, M. Piglione 2, S. Lijoi 2, A. Linari 3, P. Fania 1, E. Panighetto 1, F. Fagioli 2 CONCLUSIONS PET/CT is a useful tool in the metabolic characterisation of lesions of unknown origin, suspected for malignant disease in paediatric patients.  It improves lesion localisation  it allows a guided-biopsy, identifyng the more accessible and active sites, thus increasing diagnostic rate.  It allows to avoid biopsy in patients with a PET-CT negative for disease, with a high metabolical activity.  The combination of structural and metabolic information improves the accuracy of diagnosis and has the potential to change managment in a significant number of paediatric patients. It remains to be seen whether PET/CT can reduce the number of other studies that are requested for confirmation or exclusion of malignancy in the presence of equivocal findings. MATERIAL AND METHODS twelve patients (6 M, 6 F), median age 12, with the suspected diagnosis of malignant disease, underwent FDG-PET/CT. FDG-PET imaging was performed 60 min after iv injection of 18FDG using an hybrid FDG-PET/CT. FDG-PET were interpreted visually Guided-biopsy was performed, within 2 weeks of FDG-PET, in the pathological focus showing the higher SUVmax when a malignant disease was suspected on the basis of PET- CT exam. On the contrary, patients with negative PET-CT underwent only a clinical- radiological follow-up. AIM The value of PET/CT in paediatric patients has not yet been completely established. The most noticeable clinical benefit of combined PET/CT is the improvement of lesion localisation and the ability to apply the fused data set for planning of biopsy and/or local therapy such as surgery or radiotherapy. Aim: to asses the role of PET-CT in the metabolic characterisation of lesions of unknown origin, suspected for malignant disease, in paediatric patients. RESULTS PET-CT was positive in 7 patients. The histological analysis on guided-biopsy performed on the site with higher metabolic activity has shown: 2 NHL following autoimmune lymphoproliferative syndrome caused by FAS mutation, 3 primitive NHL and 2 primitive HL. PET-CT was negative (low metabolically active lesions) in 5 patients: 1 eosinophilic granuloma, 2 lung aspergillosis, 1 spondilodiscitis, 1 lymphadenitis. In all “negative” patients clinical-radiological follow-up (at least 6 months after PET-CT) confirmed the absence of malignant disease. Metabolic characterisation of bone e tissue lesions. Finally diagnosis spondilodiscitis. Metabolic characterisation of bone lesion. Finally diagnosis eosinophilic granuloma. PET/CT exam allowed to avoid biopsy. For contact: Metabolic characterisation of bone lesion. Finally diagnosis was lung NHL in ALPS Fas gene mutation. PET/CT exam allowed to guide biopsy (a) and assess the response to the treatments (b). 1. Positron Emission Tomography Center IRMET S.p.A., Turin, Italy 2. Onco-Hematology Department, Regina Margherita Infant Hospital, Turin, Italy 3. Histopathology Departement, Infant Hospital Regina Margherita, Turin, Italy a b PET-CT resulted able to indicate the most active and accessible site guiding biopsy. Finally diagnosis LNH.