NF1 and malignant peripheral nerve sheath tumor: Since neurofibromin is a major RAS inactivator and plays a role as a tumor suppressor, the lack of neurofibromin resulting from NF1 mutation causes disruptions in the RAS-mitogen-activated protein kinase (MAPK) and PI3K-AKT-mTOR signaling pathways, which is implicated in the tumorigenesis and tumor progression of PN to MPNST (5).