Whole-body 18F-FDG-PET/MRI as a screening tool for the detection of malignant transformation in individuals with Neurofibromatosis type 1

Malignant peripheral nerve sheath tumors (MPNST) are the leading cause of death in Neurofibromatosis type 1 (NF1). They can result from premalignant neurofibromas (NF) including NF with atypia and atypical neurofibromatous neoplasms of uncertain biologic potential (ANNUBP). Some phenotypic characteristics have been described as associated with their development. The aim was to outline our use of whole-body 18F-FDG-PET/MRI in adults with NF1, especially in the screening of asymptomatic individuals with a higher risk of developing a MPNST, and to study its impact on NF classification (malignant vs premalignant) and MPNST staging over time. Individuals with NF1 who underwent a 18F-FDG-PET/MRI between 2017 to 2021 were included, analyzing separately the screened population. Maximum standard uptake value and diffusion-weighed imaging were assessed. Biopsy/surgery confirmed the diagnosis. In all, 345 18F-FDG-PET/MRI were performed in 241 patients including 149 asymptomatic (62%), but at risk. Eight MPNST in 8 screened individuals (5%), 6 NF with atypia in 4 (3%) and 29 ANNUBP in 23 (15%) were diagnosed. Over time, the proportion of grade 3 MPNST and the malignant/premalignant ratio in screened individuals significantly decreased (p=0.03 and p<0.001, respectively). This study emphasizes the diagnostic and screening performances of whole-body 18F-FDG-PET/MRI in adults with NF1.