NF1 and malignant peripheral nerve sheath tumor: Spontaneous transition from pNF to MPNST in mouse models is relatively rare but has been observed.11,81,96,107 In the majority of these MPNST mouse models, functional deletion of NF1 and additional relevant tumour-suppressor genes directly leads to the development of MPNSTs without apparent neurofibroma formation.118,122–125 Xenograft models are attractive and widely used for preclinical studies of MPNSTs.126