Malignant peripheral nerve sheath tumors or MPNSTs arise in patients with type 1 neurofibromatosis (NF1) and are often associated with activation of the Ras pathway due to loss of function mutations in NF1, a gene which encodes the Ras-GTPase activating protein (GAP), Neurofibromin (NF) [37]. This evidence concerns the gene NF1 and neurofibromatosis type 1.