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Malignant peripheral nerve sheath tumors (MPNST) are a group of tumors arising from or showing differentiation along one of the nerve sheath elements such as Schwann cell, perineural cell, and fibroblast. In rare instances, malignant tumors arising from nerves may display aberrant differentiation, e.g. angiosarcoma; such tumors are not included in the category of MPNST.

MPNST makes up 5% to 10% of all soft tissue sarcomas. About 50% of MPNST arise de novo. The remainder from neurofibromas in NF1. MPNSTs usually occur in adults (age range 20-50 yrs; median 35 yrs.) but rarely may arise in children as well. Most involve major nerve trunks such as sciatic nerve, brachial plexus, and sacral plexus and this is reflected in locations including proximal upper and lower extremities and the trunk.

MPNST cause fusiform or eccentric swelling of the originating nerve trunk. The tumor may spread both proximally and distally causing thickening of the nerve. When arising in the setting of NFI, MPNSTs are usually deep-seated. They are large (usually >5 cm), fleshy, tan-white and have foci of necrosis and hemorrhage (as seen here). Image copyright: pathorama.ch

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