NF1 and plexiform neurofibroma: Given the elevated frequency of MPNSTs (10%–13% adults3) and their younger age of onset (~3rd decade of life4,5), NF1 has emerged as a tractable model system to define the molecular etiologies for MPNST pathogenesis, as these cancers most often arise from benign precursor lesions (plexiform neurofibromas) with biallelic NF1 gene inactivation.