NF1 and malignant peripheral nerve sheath tumor: Ref-1 and pSTAT3 were also characterised in the Nf1-Arfflox/flox;PostnCre mice that harbour combined genetic inactivation of Nf1 and the Cdkn2a alternate reading frame (Arf), which is deleted in 70–90% of NF1-associated ANNUBP and MPNST collectively.17 These mice spontaneously develop nerve sheath tumours histopathologically indistinguishable from human ANNUBP and which progress to MPNST with high penetrance.